I have just comlpeted swaping a 97 4.2 for a 99 the engine runs rough seems to pop and misfire more so from pass side bank, have went over all vacume lines and double checked spark plug wires and firing order. when motor was out I replaced plugs with new, used plugs for a 97 and not a 99, noted plugs for 99 to have longer threads. could this be the culprit ?