Z284life

Hey guys this is my first post,I have a question about my 4L60E. I was at the track about 3 weeks ago and for some reason my tranny would go from 2nd straight too overdrive in 3rd. Also after my run i was getting my time slip and I went to pull out and it felt like i was pulling a 2 ton trailer. It did this on almost all my runs and I have no idea whats causing it. I'd have to press the gas down about 1/4 of the way down before it would even move. On the street it's fine i have no problems. I installed a 3200 stall, do I have to get my computer reprogrammed for the stall? Any help would be appericated.