1992 Chevy S-10 engine misses

When I accelerate from a stop it will miss like a bad plug wire or clogging fuel filter . It doesent do it every time and plugs, wires, filters have all been replaced. When it does this it will improve if I "get on it" then resume normal driving. It doesnt seem to be getting worse but my fuel mileage is so various that it is driving me to the poor house. It doesent show any codes either. Someone said could be the cat. Converter, but wouldnt it do it all the time? Also the truck was just transplanted from arizona to missouri where we have a considerable bit more moisture. Please help soon.