I have a 08 Denali, im not sure which transmission is in it however i do know it is a six speed and has the electronic shift. I had a transmission leak on the transmission cooler lines. I replaced the tranny cooler lines the tranny filter, and tranny fluid. When adding the tranny fluid i added 3 qts before starting the truck and then proceeded to add another 3 qts after slowly adding and running it through the gears. After i got the tranny fluid level in the correct range i took it for a test drive and noticed the tranny seemed to be slipping, it seems to do it only when it is either shifting or when it is low RPM's and i am gradually increasing the pressure on the throttle. I only drove it for about 10 miles after deciding its to risky to keep going. Thoughts anyone???????