Have a 1998 1/2 ton with a 5.0 2 wheel drive. Great truck runs well when running properly. Idles great takes off well bu about 20 mph and above it will miss badly. My mechanic though it might be the distributor. I replaced with a new one . It did not make a difference. He stated that the popping sound I heard was a lean pop which could indicate a bad fuel pump. Haven't tried that yet. I was wondering if it might be a emission component that could cause the problem. I plan on using some Seafoam in the vacuum system to clean them out. does any one have an opinion.