My question is what the difference is between a shift kit and a transmission reprogramming kit? Does a shift kit just increase the hydraulic pressure or does it change the shift points and durations?

My '99 with a 4R70W trans has started to downshift slower and harder when decelerating when it shifts from 3-2 and 2-1. I just changed the trans and torque converter fluid with Mercon V about a month ago thinking it would improve, but no change, The truck has about 33,000 miles.

After reading several of the posts about shift kits/reprogramming, I'm thinking that installing one may improve this problem and give me a little better performance to boot.


//JQ