1996 Chevy Silverado random miss or misfire

The motor has a random miss while driving at various speeds and rpms. The miss a sharp, dead spot that last for less that a second. Makes the tach jump and feels like it ran out of gas for a sec or went died. Sometimes the miss goes in a series and sometimes it just jumps every once in awhile. Started when I sprayed the motor at the car wash, had a BAD miss after that but cleared up but not totally. Thought it was the coil wire, it would not snap into the cap, replaced that but it started again. Then replaced the coil, that helped but started ramdom miss agian with in a few days. Plugs look good, wires are ok. Run 87 oct gas. Truck runs perfect except for this misfire, sometimes it doesn't do it for a day or two, sometimes it does it many times on a trip to the store ( 3 miles ).