94 Automatic Transmission trouble

I have the 4L30-E THM. the 4-3 or 3-2 downshift is getting really bad. Check engine light has been on and off for a few weeks with no problems til now. Under heavy throttle feels like the engine wants to die. Backing off the accelerator resumes power. Should I suspect a sensor, PCM, timing, or ??

Only history I have is the water pump, timing belt and tensioner were changed out about 8 months ago.