If the issue popped up after a street-workout, I think I'd be looking to the engine. Did you change the timing during the tune-up? Too much advance can kill plugs. I've seen cracked insulators cause a missfire under load but idle just fine.
Hey AJ, thanks for the tip. Advanced it a hair, but really just the basic tune-up stuff, i.e. plugs, cap rotor, checked the wires etc. But I'll take a look at the plugs just in case. Thanks again man.