2000 pontiac 4t60e tranny problem

MY tranny acts up every once and awile when it has been run for half hour or more the service engine light comes on and when it shifts it shudders or jerks about 3 times when ever it shifts up a gear if you shut it off and let it cool down and the next time you drive it it will be fine even if you put on 200 mile and might not do it for a week and if your going though town and start applying the brake to stop and apply the accelerator just alittle it will drag down the motor and almost kill it then all of a sudden it will down shift.

any help or suggestions would be helpful

thanks Jim

I had just flushed the transmission it has 50,000 miles on it

any help?

I have a 1999 GP that I got from my brother because of the same problem. It will post a code P0742 lockup circut stuck on. It sometimes goes away. He gave up when the dealer told him it needed a new transmission. Odd because it doesn't slip and at times acts totally normal. But obviously the lock up is locked in.