I am noticing a hesitation and bucking under load when it gets warm. Ive replaced the plugs, wires, distributor, cap, rotor, coil, ICM and MAP sensor. It still does it. It is more evident while pulling a trailer but is constant. I don't hear the hesitation while at idle. When shifting it seems to shift out of first and quick through second gear to third. The timing is set to 10 degrees. Any ideas are greatly appreciated. I haven't been able to get a scanner to read any codes. I have an ACTRON scanner for fords from ADVANCED Auto. The problem gets worse the warmer the truck gets. All fluid levels are good. Its not overheating and oil pressure is good. I pulled a 30ft trailer and attempted to go up a mountain and barely made it. The trailer is 7900lbs. It seemed to loose power drastically when under this load. any help is appreciated.

 

You didn't mention if you checked /changed the fuel filter. How do we stand with that?

 

I changed the filter and it still is having the same problem. Fuel pressure is 32 psi at idle or at 3500 rpm

 

The one thing we did not check was the catalytic converter for being plugged.
Removing an oxygen sensor and allowing the pressure to go out the sensor hole is one way to confirm it, another way is to separate the pipe at the converter and check it that way and last if you hook up a vacuum gauge to the intake manifold and watch the vacuum as you hold the RPM at 2000/2500 RPM. If the vacuum reading drops and continues to go down there is an exhaust restriction.