I have a 96 5.0 4x4 5spd with 3.55s and 33x10.50s. For some reason it just doesn't feel like it has the power it should down low but when it hits about 3k it feels like it comes on all at once. I'm sure some 4.10s would help with the bigger tires but it really doesn't feel like that is the problem. I did an ignition tune up with motorcraft plugs, msd cap and rotor, and I'm not sure on what wires but they were decent. It also has a clean air filter, fresh fuel filter, and I've sea foamed the engine and ran fuel system cleaner through it a few times. The truck only has 65k miles and I feel like it should run a little better than it does. Any ideas where to start? Could running platinum plugs instead of copper be part of the problem? ( I did the plugs before I read to use cheap copper ones)

 

Check for OBD II codes. Check O2s for a variable voltage feedback signal (0.1-0.9 volts) from either a white/red wire or one of two black wires. Constant voltage from the O2 sensor indicates the ECU is operating in an open loop (Limp mode). If so, replace 1 or both O2 sensors.