Transmission shifts fine at normal speeds but will not downshift at any speed into kickdown at wide open throttle - no codes - transmisson was checked and PCS replaced, same problem. 1999 yukon 5.7ltr 4l60e tranny 4wd

What is your question?

I have had the tranny gone through and they replaced the PCS, throttle body gaskets, wiring harness, filter and had the same problem as before. Transmission shifts fine in normal operation, but will not downshift to 2nd for hills or passing when accelerator is depressed. Have and pretty much ALL the sensors in the engine replaced, the spider injector, fuel pump and sensors, distributor, battery, and alternator. Cleaned MAF, replaced engine temperature solenoid (as well as just about every other solenoid and switch) checked throttle body sensor, still have same problem. There are NO warning lights or error codes shown. Problem was originally intermittent then became chronic. Had p0300 codes and replaced all sensors and distributor and finally spider injector. Had p0748 code and replaced PCS, all to no avail. HELP. I have had this to THREE shops and all they do is throw parts at it and charge me a fortune to fix nothing.

What makes this problem better or worse?

only happens when accelerating up hills or passing - no passing gear

How long has your 1999 GMC Yukon had this problem?

several months