4t65e Transmissions Slips after 5 min of runtime

[CrazyBuick]

Strange problem here that I was hoping that someone might be able to help me out with. This problem relates to my DD 1998 Buick Regal GS (Supercharged 3.8 with 4t65e transmission).

Yesterday while driving down the highway, the transmission started to make that whirring noise like it was it out fluid. I knew that I needed to get off the road, and as I was pulling over, the transmission felt like it let go. I was able to get to the side of the road and turn the car off, but I was in a terrible spot and I knew that I had to at least try to get the car someplace safer. When I restarted the car, it dropped right into gear and was quiet as a mouse, hooked right up and got me someplace safe... and then it started to slip again. Subsequent testing shows that the transmission operates perfectly for five minutes then let go. Power cycling the motor (key off, wait, restart) will restore the transmission to perfect working order... for another five minutes. The transmission will cease to function normally after five minutes regardless of speed, RPM, or even sitting idle.

My first idea is a clogged filter. Next is a Pressure Control Solenoid. After that, a failing ECM? Is there anything else that could cause this behavior? Any suggestions on how to diagnose and determine which item it could be?

Appreciate any insight.