1994 Ford Ranger

Other Category problem
1994 Ford Ranger 6 cyl Four Wheel Drive Manual 150k miles

I am at my wits end with this problem. My 4x4 94 Ranger w/4.0 engine becomes unresponsive to the throttle at highway speeds. I can be cruising along at 60mph and the engine losses power and rpms start dropping off. I have to down shift and pump the gas to get speed back up. Or sometimes it will buck and not accelerate while in low gears, say while taking off at a light. I have replaced the following: fuel pump, fuel filter, fuel pressure regulator, throttle position sensor. Plugs and wires, air filter, pvc valve and none of these has corrected the problem. I am also getting terrible gas milage. I have looked at the computer codes and they indicated that both banks were running rich and lean. And that there was a 502 or something with the ground with the fuel pump. I have replaced the pump. I do not have a check engine light on either. Please if you can steer me in the right direction I would appreciate it. Thanks.