I swapped a 92 corvette LT1 into my 89 chevy pickup. A hybrid harness was made for me by Speedscene in Texas. The truck used to run awsome, (thrashed 2x4 Hemi Dodges no problem) but now there seems to be a speed/temp related miss. The truck will run great on startup, but after driving for 5-15 minutes the truck develops a clear mis throughout the RPM range. Plugs, wires & optispark are all new, fuel pressure stays between 38 and 45 psi (depending on vaccuum) and there are no codes/check engine lights. Everyone blames the optispark, but it is new and I have since taken it apart and inspected it; no moisture or dirt. Help???!!!