does this truck have any sort of "dot-lock" installed? this sounds like a dot-lock traction controller out of calibration. you may need the software and cable from dot-lock to be able to calibrate it.
you say this is "straight gas"?
I did not know MCFA made any "straight gas" trucks in this size range after tier 1, although they did make some dual fuel.
Also, as far as I know, all the MCFA gas units after tier1 require high octane gas, or they don't run well.

also, are you SURE that at the time it has no accel function, that it has no code right then, that resets? ?p22?
also, check the wires in the plug to the accelerator pedal position sensor (foot pedal pot)