I had a slight misfire around 45000 miles. So slight that you could barely hear it in the exhaust. I drive nothing but highway, about 100 miles a day, so at high RPMs it was barely noticeable. It finally threw a code (misfire..duh) around 50K. I checked the plugs, all looked clean, etc. So I brought it to the dealer. The number 3 cylinder was misfiring. Cause was a clogged injector. But that is was just the beginning. The reduced fuel into the cylinder brought the temperature up in that cylinder. The temperature got so high that the valves and head started to deform. I ended up needing a new head (too deformed to machine the existing one) and valves. Probably some other things too, I don't remember exactly what. I believe them because they showed me everything. The main concern GM had was that the Ethanol in fuel may have contributed to the increased temps. They wanted all the parts sent back so they could research it.
Then came the 'who pays' part. The injector was the ultimate cause and was not covered by the power train warranty. But the car is a PZEV and I live in one of those states that requires those vehicle to replace anything that would cause an emissions rejection to be replaced under warranty if I am the original owner. So I didn't pay for it and have no idea how expensive it would have been. Also got a free rental for the week it took to get done.
Hopefully your issue is a bad plug or one of the coils.