x2 i have a manual but my buddy has an auto and he drives it with OD on with a similar set up. The truck will tell you if it wants to shift or not, if your constantly downshifting out of OD then i would say run with it off. But with 3.73's at 75mph you shouldnt have a problem staying in OD on flat ground and even hills you could climb depending on how big.

 

Maybe mines different but I live in Illinois (doesn't get much flatter) and my jeep hunts and downshifts on the interstate because it can't hold the speed real well with od on. But ya totally up to you and how you want it to drive

 

did you recalibrate your speedo with a procal? The aev procal recalibration will change your shift points not sure if all of the recalibration tools do the same. Also maybe your motor is a little weaker then some. I agree if you can not hold speed or are hunting for the proper gear then you need to downshift but if you are maintaining speed and not hunting then no reason to downshift.

 

Nah my op said I've been runnin without one...why idk just never got one but its on order now from Northridge so it'll be interesting to see what it does for me.

 

might be your problem right there.