Engine misses when weather is hot & humid!

Maybe someone can help me brainstorm the possible cause? I have a misfire going on that only happens when it's hot & HUMID out. Ocassionally when it is raining also. When the miss isn't there, the engine runs perfect, and I have yet to get it to throw a code, even yesterday when it was missing badly. It doesn't do it as badly at light throttle as it does with heavy throttle. I have replaced plugs, wires, and ignition coils. I'm really having trouble figuring it out without a code. I'm over 100k miles, with the original cat, but I thought if they got clogged it would throw a code. Any ideas?
-John

If it misses in damp weatehr I would lead towards ignition wires? Check them see if their is anything wrong with the wires(cracks, rips, whatever).

I've checked them, and everything looks fine, but this problem persisted even immediately after putting on the new plug wires. Normally when I've had an issue with a plug wire it resulted in a code being thrown. Would a sticky injector throw some sort of code? The miss is more than noticeable, but still no code!