Mystery Engine problem

I have a 1989 Mustang. If you floor the accelerator pedal the car will very shortly start to act like it's running out of gas or losing spark. It won't hold speed and starts to slow down. If you down shift and ease into the throttle slowly it will run very ruff for a sec then start to run ok except that you still can't eccelerate or climb hills without a repeat performance. If you turn off the engine then restart the problem goes away until you forget and step into again. If you never floor it the problem never happens.
I've already cleaned and later replaced the TPS and I've tested the Map sensor, O2 sensor, IAC valve, and pressure tested the fuel pump at the manifold. All are within specs. Exhaust checked for plugup and excess back pressure too. Vacummn system with in spec's also. Any ideas????? thx

There is a wire that goes from your distributor to the positive side of your battery. Disconnect it and set your timing at 10* at idle that’s where mine is and then re connect it. If you try to adjust your timing with out doing this it will re set it self. Try this and check your air filter to.

Did you check your coil?

change your fuel filter.. lol