1996 Camaro RS 3.8 with miss fire codes

I have a 1996 Camaro RS with a 3.8 with 215,000 miles on it. The car will miss fire and store the code for a miss fire. It will then run good. When it goes to the shop, they see the miss fire code and the car is running good. The EGR valve was bad, replaced it. The plugs bad, replaced it. The coils bad, replaced all 3. The wires bad, repalced it. What else could it be?

HELP!

With every thing else replaced and you still get the code P0300 (random multiple mis-fire) it would either have to be the crankshaft position sensor or the ignition module.