Just a FYI: Compression is normally between 150-180 PSI(pounds per square inch) so if you do run a compression test and it is lower than 150(2-3 lb variance) then it is one of three things. 1.) burnt valve; 2.) gasket failure right at that particular cylinder; 3.) O rings on piston are worn and is allowing for miniscule amounts of oil\air to pass thru. The best way to tell if you have oil leaking around your O rings is pull the spark plug. If it has oil residue on it or you can smell burnt oil on the plug then it's going to be your block.

Hope this helps.

Plugs rarely cause a misfire. Bad gas mileage yes. Try swapping plug wires first and see if the misfire follows the swap. If it does, you still need a tune up, plugs wires, cap, and rotor. If it doesn't, pull the plugs and do a compression test on it. If it is within specs(sorry, I don't know the numbers). Then do a tune up. Look at number six plug. Causes for the plug to misfire would be, Cracked ceramic, fouled out from oil, and in some cases the electrode is completely burnt away.