[weswisehart]

I have a automatic 5.9 96 1500 4x4 I recently purchased. While try to get up to highway speeds it backfires, has lack of power and acts as if it wont change gears. Once i get to 70 and hold that it seems fine. The moment i slow down it will backfire and lack power. The rpms will be high and the truck wont speed up.

I have bought and changed the distributor cap, spark plugs and wires, crank position sensor, throttle position sensor, coolant temperature sensor and no change in performance

 

[Warlock III]

Where does it backfire from?

Intake?

Exhaust?

 

[macez]

Does it throw any codes. I would check your o2 sensor.

 

[Oatess85]

Im not able to provide any help but my truck does the same thing. Ive been told to check the pan gasket for leak, cat converter, plug wire routing, and clean the throttle body and check for cracks