97 lumina acceleration problem
 

i bought a lumina from a guy and it came with the wonderful engine tick and a leaking exhaust manifold and crappy acceleration. so heres what it does, when the car is first started it runs fine till it starts to warm up after a few minutes then when you start to accelerate it doesnt really want to (almost as if its not getting the proper fuel) but if you put it to the floor it goes down the road just fine. i replaced the plugs, wires, fuel filter and switched the coils and cam sensor from another motor i had laying around and it still does it. i clean the fuel injectors with a on the rail fuel injector cleaner and no change. do you think i have a injector going bad?? i was going to test them but needed to take the upper intake off and thought id check here first.
also can i check the resistance of the injectors from the harness connection?
thanks

Check your mass air flow sensor

I put a new fuel pump in it this weekend and the same results. I checked the fuel pressure and its still running at 40psi why would that be? It should be 41-47psi

I will check that also. It only runs like this when u drive it, when it sitting at idle and u rev it up it sounds just fine but as soon as u put a load on it that's when it runs different