1997 2wd Pickup Backfire Problem

I have a 1997 Chevy p/u with 110k miles with a 350 engine. It has begun back firing intermittently while starting. The engine will run rough for 30 - 45 seconds then run normally. When this happens, the check engine light comes on and a P0300 trouble code (random/multiple misfire) is stored. I have checked the plugs and resistance on the plug wires and everything is normal. No other trouble codes show. I'm not quite sure what to check next. Any suggestions would be greatly appreciated. I am concerned about a backfire damaging the catalytic converter.

Regards,

Phil

Did you check the cap and rotor??