99 Yukon engine misfire

I am getting a misfire code on #5 cyl, The rep. said to rebuild or replace engine. Was a little reluctant on doing that so I ask for a compression test to be done. They said that would be $120 so I said OK.. No. 5 was 140lbs and adjoining cyls was 150. I asked what the dif was between the wet and dry and he didnt know what I was talking about. After several calls he got with the mech. and he said they done wet/dry on #5 with no diff. also a leak down test showed it was bad rings. With these responses I dont know how good of a job was done on the tests. I replaced the plugs and the light goes off for a while and then on for a while. My biggest question is how to rule out other possible problems before moving on to the bad rings. Such items as EGR valve, bad ignition, fuel, etc.