1993 Chevy Astro 93 Astro tbi - poor acceleration

When I step on the pedal, the van starts to die, kicks and sputters. If I push all the way to the floor, it downshifts and accelerates OK. When it upshifts again and I step on the pedal again it wants to die. Idles great.

I have replaced O2 sensor, PCV, EGR, map, ignition control module, fuel pump, fuel filter, temp sensor, and many other things. No vacuum leaks. Fuel pressure OK.

When I first start the engine cold it will run perfectly for 5-10 seconds when the outside temp is fairly warm. In the winter, it will run great for 10-30 seconds. If I shut it off and turn back on it will run perfectly for 5-10 seconds again. I think it has to do witha bad sensor or something.

Heres another thing. When I remove the gas cap for a fill up or any other reason and then replace it, it will run even worse. Eventually it will run better until the gas cap is removed.

Help