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CTT tuning on 18 deleted w/ 40's

8K views 91 replies 19 participants last post by  nick00less 
#1 ·
I have a 2018 that has been fully deleted. I have stock gears and 40" tires.
Before the delete I had the 40's on for 30,000 miles, it did not shift bad but was not great until I corrected the speedo with the AEV procal. After that everything was great! Drove great, shifted perfect and was getting about 16 mpgs in town 18 mpgs on highway and 13 mpgs towing. I was pleased but thought it would be great if I could get better mileage. I deleted it and tunned with ez lynk and CTT. It shifted horrible, could not get it to go to 6th until 80mph. After many many tunes I got one that is ok, shifts into 6th at 58mph at part throttle, but seems to "float" between gears for a while and is worse towing. I have asked the tech at CTT about this and he says he does not know what to do. He sent me another tune but it did not work.

My goal here is long life, good drivabilty and great mileage. I am open to ideas.
 

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#8 ·
Right so we have gotten the negative out of the way. Re gear will definitely help with everything.

Do you have trans tuning? If not that will help as well. If you do then try having your shift point adjusted to your liking. CTT usually has very good reviews and trans tuning so hopefully they get it lined out. But your biggest improvement will be new gears.

Edit: Also a big welcome to you sir. Lots of good info here dont let a lot of ribbing turn you off.
 
#16 ·
I figured everyone would say to re-gear. I hate to change the gearing because of the mileage I am getting. And YES they are 40's and yes those are real mileage numbers.
They transmission was absolutely perfect before the tune and now it is not. I have a stock transmission tune on it now but it is not the same as it was.
 
#19 ·
That $6,000-$8,000 transmission is going to not make that fuel mileage look so good!! Your high gears and 40's are killing your transmission.
 
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#21 ·
Can we get some kind of tutorial or sticky post about how important gearing is for literally every aspect of using a truck? Towing, MPG, drive ability, I get the email of "trending posts on cummins forum" and 4 of them today were self induced problems due to tires too large and stock gears. If you have larger than stock tires, you need lower gears. Period. Doesn't matter how much torque or what programmer or tuner you're using. None of those changed the loss of efficiency when your gears are too tall. I wish there was some kind of survey on how many guys moan about their 68RFE problems and how many of them have 37s on stock gears.
 
#22 ·
Doesn't matter how much torque or what programmer or tuner you're using. None of those changed the loss of efficiency when your gears are too tall.
Umm, I have to warn you. It's not always popular to bring up the basic laws of physics here.
Just sayin'.
 
#28 ·
IDK what they teach now a days but I know that there a lot of misinformation about lower gear ratios. Everyone seems to think it hurts mileage, It usually helps with mileage when running larger tires. Thats why I think we need a sticky on it. Maybe even Nitro Gear would sponsor it. If you read the REVMAX information on their 68RFE, it says they don't warranty transmissions with larger tires unless you have proof you regear. Thats evidence enough.
 
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#29 ·
This should be a fact but people dont belive facts anymore. Everyone is smarter than anyone else that's also a proven fact. People that dont understand will run with the crappy gearing and say it's fine. That then becomes fact so everyone else believes it. Until people experience proper gears for themselves they just dont understand what they are missing.

There will always be the type who live by, well I did it this way and nothing bad happened so I did it correctly. When typically they just got lucky.
 
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