ok I have a 1998 K1500 5.7 that keeps throwing a #5 misfire code. I've changed the Cap Rotor Wires and Plugs....nothing changed....It has a consistant misfire at idle and when it's in overdrive under load like going over an over pass or up a hill on the interstate....I've checked the plug and it's white with a little build up............It started doing this after I changed the fuel filter ...before that the check eng light never came on.. it idled fine and accelerated fine....What's the problem?

 

you may have a clog/dirty injector. check compression on that cylinder also

good luck