I have a 94 silverado and when I warm the truck up I notice a slight miss.I can see the Tach go down a little like its missing.Its got new plugs,wires,fuel filter,cap,rotor,all within the past 3 monthsso im wondering whats the miss? It still runs good and drives fine with no problems. And there is no check engine light. Is it the MAP sensor,TPS. Wondering what it is. Its got 292,000 on a 350 5.7.Help.