Hi, i just joined this site, i'm looking for some opinions on what can be ailing my 1999 Dodge 3/4 ton, it has a diesel cummins engine, i just put a 2'' levelling kit on the front for clearance for the p315/75/16 BF Goodrich AT's, as soon as i installed the tires the transmission is shifting in and out overdrive, had the computer recalibrated, didn't seem to work, any suggestions???? thanks mike  

Yes, axle ratio.  You changed the effective gear ratio with bigger tires. (many seem to ignore this) This has resulted in a higher torque load being needed to cruise now and tranny is sensing it and down shifting to meet demand. The proper way to fix this is to regear axles. Forcing tranny to deal with it otherwise can shorten it life especially if you tow with it because that is not exactly the strongest tranny behind a diesel out there and lugging it can takes it toll as it is not very forgiving stock.  

Thanks for your info, and i don't mean to be dumb here but just how do i go about regearing the axles, do i need to change them? thanks again mike  

No such thing as a dumb question. To regear axle you have to replace the ring and pinions in the front and rear axles which can get pricey if you go to a dealer. The gears themselves can be had on line for less than 500 bucks and figure another 500 to 800 bucks total labor to have them installed. Below in a link to a Tire Size and Axle Ratio Calculator that I host that you can play with the numbers. Feel free to use it as much as you want, when ever you want.

Click Here  

Thanks alot, i'll keep u posted how things go, cheers mike