96 chevy c3500 7.4 gas motor

[Web65]

Truck started running like it had a misfire. Give it gas and it wouldn't hardly go. But when it would it ran like it should. Then it started like a misfire or vacuum leak. Changed plugs, wires, rotor and distributer cap. Also fuel filter. Now it's like it's worse. Tach jumps up n down a few hundred rpms while driving. Once I get on road and get it going still acts like misfire or vacuum leak. All vacuum hoses are good. I cleaned the idle control sensor of the carbon build up. No change. Also MAF sensor along with the little sensor before may but it doesn't run or dies when I plug them up. Need help please. This is my work truck n I need it.

Thanks

[Jsdirt]

I'd be looking at fuel delivery. Is the pump supplying the correct pressure and volume?

 

Next common issue on the list is intake manifold gasket vacuum leaks, or any other large vacuum leaks (Brake booster hose / booster itself, other vac hoses, etc.).

 

Normally these leaks make the vehicle run worse at part throttle rather than full throttle. If she runs strong with the pedal to the rug, idles perfect,  but misfires / hesitates at cruise, that's a dead ringer for an intake vacuum leak.

 

If it falls on it's face whenever you give it any pedal, then I'd look at fuel pressure / volume. Filter clean, lines clear, pump GOOD, etc..