1998 Ford Mustang Engine Problem

I just bought a 1998 Mustang from someone about 100 miles away, drove it for about 3 1/2 hours to get it home without a problem, no overheating, no low oil pressure, nothing even though there was check engine light on. The car seems to shake when it's idleing and my dad said it was because of a misfire. A few days ago we used his OBD-II tester and it showed two codes, one was Cyl. #2 misfire, the other was because it had overheated in the past. I changed the spark plug as well as the wire and it hasn't resolved anything. My dad said it could also be a bad head gasket. There's no funny exhaust such as white smoke. Only problem I find is the car doesn't seem to have the power it should. Any help would be great. Thanks