I have a 97 GMC with the 5.0 5-speed. The other morning, we had a cold snap. The truck ran fine on the way to work. I let it idla for 10 minutes several hours later,everything was fine. Then in the afternoon, when I started the truck to go home from work, Igot a check engine light and the truck ran rough. Above about 2500 rpm, the light flashes. When I return to low rpm it comes on solid. I had it scanned and the #1 cylinder was misfiring. My guess, condensation in the distributor. I replaced cap,rotor,wires&plugs.They needed it BAD! Light went off .Truck smoothed out. About 3 minutes into test drive, it returned doing the exact same thing, but the truck is still running smooth. Any guesses?