I've had my lift and 315/70 duratrac a on for a few weeks now and I'm a little concerned about it shifting out of fifth. I have a 13 auto with 3.73 gears. I've noticed under mild acceleration when shifting gears it wants to hold on all the way up to 5000 rpm before shifting. And now on a very mild grade at highway speeds it always downshifts where it never did this stock. Am I being paranoid or is this normal? This is my first jeep and lifted vehicle. Thank you in advance!!

 

Did you use a Procal to set the tire size?

I can't remember if setting the tire size also updates the shift program and shift points, but that doesn't seem relevant here. It will just feel a little sluggish, and not hold gears out to 5,000 for no apparent reason.

You might have a little bit of hunting between 5-6 on light grades. A 315 is a much bigger tire to push over a 255 and tire size affects your overall gearing. Bigger tires make your gear ratio numerically smaller (i.e. 315's will make your 3.73 gears "feel" like they are actually a 3.21).

 

Ya used pro cal. Tires only measured about 33.5 inches and it accepted it fine. Speedo is dead nuts on according f to GPS too.