99 Firebird 3.8 Cyl 5 misfire

I recently replaced my plugs and wires on my car. Three days ago i was driving on the freeway and the engine started to skip and the check engine light went on, i hooked it up to a OBDII scanner and code p0305 came back. I checked the wires and everything seems to be connected right. i cleared the code but the engine keeps skipping. Any other suggestions? My car has 116,*** miles on it