HELP!!!! 4.0l engine problems

[kas5267]

I have I 99 B4000 M/T, flowmaster muffler, magnaflow cat, K&N FIPK II intake. My engine is lacking power throughout the rev range but is most notable on the highway. I have trouble maintaining 65 if there is even the slightest hill, which usually requires downshifting and putting it to the floor. The truck keeps burnin out plug #4 and every once and a while throws random misfire codes. The truck struggles to rev after about 3500. Every once and a while the truck will run very rough when it is first started up and sometimes stalls out. This seems to go away if I replace the plugs but always returns eventually. I have replaced the following parts in search of fixing this problem.

Coil pack
Plugs
Wires
Injectors
Fuel Pump
Fuel pressure regulator
Fuel filter
Crankshaft position sensor

any help would be greatly appreciated

 

[trader007]

could it be a bad knock sensor? just a guess. it almost sounds like its not adjusting timing as you rev it uo...

 

[kas5267]

Where is that located?