The guys at H-1 did an excellent job of diagnosing the problem with my gmc pickup. The truck was lacking power and the idle was low and erratic at times. (rpm would raise and lower). At times also the rough idle would cause the engine to stall at stop lights and signs.The majority of the problem has been solved with new plug wires thanks to one of their techs. The truck still has a slight rough idle issue in which I will contact H-1 soon and I am sure they will be happy to resolve the remaining problem.