2001 GMC jimmy misfiring issue

I have a misfiring code on cylinder #5 code po305.I have just recently replaced the fuel pump no codes before fuel pump change. During the troubleshooting process on the fuel pump issue I sprayed starting fluid in it and it backfired through the throttle body. Went ahead and changed the fuel pump and now I get the misfire code. I have changed the plugs,wires and distributor cap and no change. I have performed a compression test on that cylinder and holds pressure,just trying to rule out blown head gasket.
Any other suggestions on what may be wrong before I turn it over to the local stealership?
Thanks for any and all help resolving this matter.