1999 Trans/Am with a 4L60 Transmission bolted to a 5.7L engine.
The trans slips in 4th gear when it is ran for 35 minutes or more. I have been through the trans and it is sound. Could this be a programming problem? The trans is rebuilt and had this problem before the rebuild but when we got into theTraining is was burnt out. We used High energy parts and replaced the sun shell. The pumped checked as good so we reused it. What is your opinion. Maybe throttle switch?

Optional Information:
1999 Pontiac trans/am 5.7L

Already Tried:
rebuild