[GoldCountryCA]

I have a 04 2500 QCLB with an nv5600. I’m having ARBs installed in a couple weeks. So if I am going to regear, now is the time. The truck will live with a very light camper in the back most of the time and will have a fairly light horse trailer behind it part of the time.

I’m strongly contemplating going from 35” tires to 37” tires for greater diff clearance off road.

If I stay with 3.73s on 37s, 6th gear is almost useless unless I’m doing over 75mph. If I go to 4.10s on 37s, I’m screaming in 5th gear up grades to keep up with traffic.

I guess the important question is this… Is sixth gear a bad idea with the load a slide in camper imposes as much as it’s a bad idea when towing? I’m talking from a longevity / durability standpoint with the nv5600.

Here is a list of RPMs at 60mph in 5th and 6th gear:

With stock 3.73s on 35”—

2150rpm in 5th / 1610rpm in 6th

with 4.10s on 35” —

2360rpm in 5th / 1770rpm in 6th

with 3.73s on 37” —

2030rpm in 5th / 1520 in 6th

with 4.10s on 37” —

2230rpm in 5th / 1676 in 6th

 

[Ram-vet78]

I have a 16 w 3.73s and 37s and it's perfect. I'm at 2000 at 73 mph. I know I'm comparing a 5.9 to a 6.7. If I had 4.10s it would pull like a beast but would limit top speed. I'd be at 2200 at 75 w 4.10s and 37s. The g56 and nv5600 have similar 6th gear ratios so you should be in a similar situation. If you're gonna be keeping it to 70-75 4.10 will be good w 37s and towing/slide in camper. I think you could get buy w 3.73s but 4.10s would be ideal. The big issue will be what speed you wanna travel at.

 

[98whitelightnin]

I have a 16 w 3.73s and 37s and it's perfect. I'm at 2000 at 73 mph. I know I'm comparing a 5.9 to a 6.7. If I had 4.10s it would pull like a beast but would limit top speed. I'd be at 2200 at 75 w 4.10s and 37s. The g56 and nv5600 have similar 6th gear ratios so you should be in a similar situation. If you're gonna be keeping it to 70-75 4.10 will be good w 37s and towing/slide in camper. I think you could get buy w 3.73s but 4.10s would be ideal. The big issue will be what speed you wanna travel at.

Did you swap in those 3.73 or did g56 trucks come equipped with them?

 

[GoldCountryCA]

I have a 16 w 3.73s and 37s and it's perfect. I'm at 2000 at 73 mph. I know I'm comparing a 5.9 to a 6.7. If I had 4.10s it would pull like a beast but would limit top speed. I'd be at 2200 at 75 w 4.10s and 37s. The g56 and nv5600 have similar 6th gear ratios so you should be in a similar situation. If you're gonna be keeping it to 70-75 4.10 will be good w 37s and towing/slide in camper. I think you could get buy w 3.73s but 4.10s would be ideal. The big issue will be what speed you wanna travel at.

On average 60-70mph. I’m in no hurry to get down the road.

I’ve been reading quite a bit about the pitfalls of staying in 6th with a load both for the transmission and EGTs…

 

[Ram-vet78]

I had 3.42s w 35s and it was good. I swapped to 37s and it just didn't feel right. It was Ok, and it towed OK but no where near ideal. So I went back and forth between 3.73 and 4.10. The 3.73s were perfect. I'm sure 4.10s would be more fun but they'd be a little much on the highway. They would have been spinning 2200 at 75 and I'm usually 75-85. The 3.73 w 37 put the engine in the same spot at the 3.42 and stock tires (about). I know I'm giving my experience w a 6.7 and the OP has a 5.9. I'd bet the 4.10 w 37s would work well between 60-70. You should have full use of 6 gear.

 

[Red and Black]

On average 60-70mph. I’m in no hurry to get down the road.

I’ve been reading quite a bit about the pitfalls of staying in 6th with a load both for the transmission and EGTs…

So for from 35s to 37s you are only gaining one inch of ground clearance. Is the price for gears, labor, supplies, etc. It is worth it?

I mean, if you have a hole in your pocket, go for it!

I never lug my truck with a load. Especially up hill. 6th from what I understand is OD and not so strong. Good for flat ground, down hill, and bob tailing. Under a load (if you don't have an EGT, get one! AutoMeter makes a nice one) in a high gear will cause problems. The engine is an air pump of sorts. If it does not have enough air flowing through it, it will get hot. That is why when I run the piss out of my hotrod, I leave it in gear and let it pump fresh air in as I slow down. Get an EGT, you will see the difference.

 

[Ram-vet78]

if the OP is rebuilding that diffs either way there's really no price difference between buying different ratios. New 3.73s or new 4.10s is close to a wash. Most people won't reuse old ring and pinions if they want it to be reliable in the long term. The traction I gained w the 37 off road was pretty significant, especially aired down. If doing front and rear ARBs adding 37s will only make it more capable and the new gear ratio will complement the setup well.

I make sure you get AAM gears and timken full bearing kits. It's a little more than nitro stuff but better quality. I got my stuff from west coast gear. It's not a cheap project, but it will make a massive difference in the capability of the truck.

 

[GoldCountryCA]

So for from 35s to 37s you are only gaining one inch of ground clearance. Is the price for gears, labor, supplies, etc. It is worth it?

Exactly what Ram-vet78 said below. I’m already almost $5k into adding ARBs front and rear; $800 for new factory R&Ps is not a deal breaker. I’m very blessed and not really stressed about the money I’m putting into the truck.

I definitely plan on upgrading the monitoring situation. I’m doing a smarty with Egt and also adding some ISSPRO gauges for a couple other things…

if the OP is rebuilding that diffs either way there's really no price difference between buying different ratios. New 3.73s or new 4.10s is close to a wash. Most people won't reuse old ring and pinions if they want it to be reliable in the long term. The traction I gained w the 37 off road was pretty significant, especially aired down. If doing front and rear ARBs adding 37s will only make it more capable and the new gear ratio will complement the setup well.

I make sure you get AAM gears and timken full bearing kits. It's a little more than nitro stuff but better quality. I got my stuff from west coast gear. It's not a cheap project, but it will make a massive difference in the capability of the truck.

I do believe it will work very well for what we need it to do. We just did all the goodies from CJC for a 2” kit from thuren/fox last year, but have since decided to go full king pintop 3” kit from Carli with Carli torsion sway bar, 6 bolt psc box/ mopar power steering, etc. this go round.

Not looking forward to trying to free up the loctite red I just put on the Carli track bar last year. I may just buy another track bar and keep the existing one with the 2” stuff in case I find someone who wants those items as a package.

 

[98whitelightnin]

I’ll be interested to hear the difference in ride difference in Thuren and Carli. I’ve had multiple trucks with Thuren and always say I’m gonna give Carli a try but never do because I don’t want more than 2”.

 

[GoldCountryCA]

I’ll be interested to hear the difference in ride difference in Thuren and Carli. I’ve had multiple trucks with Thuren and always say I’m gonna give Carli a try but never do because I don’t want more than 2”.

That’s specifically why I went with the thuren coils and fox shocks tuned to the thurens. I only wanted 2” last year w/35s. Someone will get a smoking deal. I have five 35” Nitto ridge grapplers with about 4000 miles on them and the shocks and springs have the same mileage as well.

 

[GoldCountryCA]

At what load does 6th gear become problematic? Should it be a consideration with a 1500 load in the bed or is it only a factor when towing a decent amount, such as 7500lbs plus?

Depending on that, I may primarily look at 1-5 and 3.73s would make much more sense.

 

[Ram-vet78]

I use 6th gear all the time towing and loaded. It's really just like any other gear, it's about the load on any gear. If you're lugging it it's gonna lead to issues. I'll tow 5-10k lbs using it all the time. I down shift when I need to. I keep it above 18-1900rpm in 6 while towing. I usually like it around 2000-2200 w a load. But as the load size goes up I drive slower so I'll use 5th more. With the old g56 w the lower gearing in OD and 4.10 w 37s I think it would do really well towing 60-70. I'd imagine that setup will allow a srw truck to tow well near its max drivetrain wise. Now suspension wise, that's another deal. I think the EGT sensor is the move, especially if there are any mods.

 

[GoldCountryCA]

I use 6th gear all the time towing and loaded. It's really just like any other gear, it's about the load on any gear. If you're lugging it it's gonna lead to issues. I'll tow 5-10k lbs using it all the time. I down shift when I need to. I keep it above 18-1900rpm in 6 while towing. I usually like it around 2000-2200 w a load. But as the load size goes up I drive slower so I'll use 5th more. With the old g56 w the lower gearing in OD and 4.10 w 37s I think it would do really well towing 60-70. I'd imagine that setup will allow a srw truck to tow well near its max drivetrain wise. Now suspension wise, that's another deal. I think the EGT sensor is the move, especially if there are any mods.

I’ve never had a nv5600 apart, but sixth gear is apparently much weaker than fifth. From reading, sixth gear failures are not uncommon. They are supposed to be babied somewhat. It may be overblown, but I’m not an expert by any means…

 

[Ram-vet78]

I think the overdrive issues were more w the nv4500s and less with the nv5600. Either way, I'm mindful what kind of a load I put on any gear. Driving w a slide in camper should have minimal/no effect on your ability to use OD. The slide in and a 2 horse trailer you'll still be pretty good but definitely be a little more careful. If you have a 6-8 horse trailer it's a different deal. If you're tuned and you try and pull a heavy load up hill in 6th you're gonna have more issues. Just be cautious w how you're pulling and you should be cool. Also keep an eye on the fluid condition. You can add coolers if you want.

 

[Red and Black]

I never pulled up and down hills. I have an 01 3500 with the HO motor and 5600 with around 200K on the clock. I have pulled a grain tender with a total weight about 20K, plus it was high profile and caught a bunch of wind. It would pull fine in 6th, but then again, I was pulling heavy, but not hills, all flat. After a while of using it on the farm and pulling boats and stuff across the country, it has some wear. You have to coerce it into second without grinding, and the same in sixth for some reason???? The only problem I have had is the roller pilot bearing locked up and messed up the input shaft. Had a brass one machined and off it was going again!

 

[GoldCountryCA]

I’m really still torn between 4.10 and 3.73. I played with an online gearing calculator for way too long last night.

 

[Ram-vet78]

I have 3.73s /37s and am at 1950 at 76mph. And about 2200 at 85. Your nv5600 should be similar. It's perfect for the speed I drive. If your gonna stick to 60-70, 4.10 would be good and easier on your trans.