1996 Lumina sedan 3.1 V-6 misfire.
 

I recently replaced the head gaskets and cleaned up the top end on my 96 Lumina. I found while taking off the heads that a head gasket was blown between cylinders 1 and 3. Now that I have had it back together for a while I have not been able to correct a misfire the engine is having on cylinder 2. It has new plug wires, plugs, and coil pack. What stumps me is, when I floor the accelerator the engine hits on all cylinders and runs great. But, when it goes back to normal driving speeds or RPM's under 3000 it goes back to misfiring. Any suggestions as to what is causing the misfire. All the fuel injectors were clean when reinstalled with the fuel rail.