Car bogs or dies when accelerating. I can't figure it out!!!

When pushing on the gas, the car bogs down, or dies. If you get up to speed slow, its fine. Giving it constent gas, its also fine. But if you let off the gas, and push it again, it starts over. I have changed
Fuel pump
Fuel filter
Fuel injectors
MAP sensor
Air filter
O2 sensor
Throttle control piston and sensor
My brother changed the comp and a couple other sensors. Can't remember the ones he changed.
I also changed the spark plugs and wire.
I have no idea what to do now. I have had a couple of mechnics also look at it. They didn't know. The car is a 1990 Pontiac Grand Prix SE, with a 3.1T motor. It also only has 100,000 miles on it. I'm going broke, so any help would be great.

Rent a fuel pressure guage from advance or oreilley's and check fuel pressure. Report back with your numbers of fuel pressure key on engine off, and engine running at idle.

What about the catalytic converter or muffler? Your symtoms sound more like these would be your problem.

Thanks guys. I'm gonna check the cat out today.

My Brother said he checked the fuel pressure gauge, and it was around 40 off, 45 on. Like 37.6, but could remember exact numbers. Have not tried the cat yet, and the 02 sensor wasn't changed. My mistake. Could it be the 02 sensor? We also found no breaks in the wiring, it all looked good.