Well, my original thought was you were putting more miles on than your odometer was reading, hence the low mileage.It's actually not.
They got it as close as they could at the dealership. So at 65 I'm actually doing 68 via gps
What are u thinking
Actually the 4.10 should be helping some with the larger tire. Stock with 3.73 and 35 with 4.10 are almost identical overall drive ratios so you are really only being hit by the extra width. Now if the tires are mudders they will get worse mileage than an AT which gets worse mileage than a street tread.I would guess the 4.10 gears and the large tires are costing you a couple . 4.10 gears are making the engine turn at a higher rpm when driving and the larger tires although the help fight against that a little they still have un-sprung weight and cause the engine to work harder to turn them. Also I don't know how you drive but an aggressive driving style will effect your mpg also.
Interesting.... I have read on here somewhere that shifting below ~1500 in higher gears puts more wear and tear on the clutch. Any truth to that?Driving "like an old man" is in the eye of the beholder. I practice progressive shifting, never above 1500 rpm and always start in 1st. VERY slow off the line but makes a big difference driving in town. You can do the same with an auto too. Just go really light on the go pedal and watch the tach. The trans will upshift at lower rpms if it doesn't sense much engine load. Try to make it upshift as low as possible. And as you've probably heard a million times, try to keep your highway speeds under 60mph as much as practical. Cummins has a really good white paper on fuel economy. Lots of good info in there.