I have a 96 Cheyenne with a vortec 350 and have recently done plugs, wires cap and rotor, fuel pump and filter within the last 5,000 miles. When I'm driving around town truck runs fine till I get up to 70mph then it starts misfiring and engine light flashes till I slow down. The code stored is the p0300 random misfire, I can't seem to figure out what could be causing it, truck has almost 180,000 miles on it. Any suggestions would be appreciated