2000 ranger 4.0 symptom when driving and accelerating it runs “normal”. When trying to hold a steady pace it bucks shakes.
Checked fuel pressure and it’s zero with the key in the on position . And it’s 68 psi and steady while running. It immediately drops to 10psi when ignition is turned off.

Any help would be appreciated.

 

You have returnless fuel system. That 68 psi is good but your "at rest" pressure of 10 shouldn't be. Since there is also no fuel return line, the injectors, fuel filter, and the fuel damper (which is used to smooth out fuel pulsations from the pump and injector) will determine the delivery of fuel to the engine. It should not leak down. Possible leak-down issues could be either a defective injector bleeding through the solenoid and/or a defective pump check valve in the pump itself...

Hope you get it figured out