Code P0304, Cylinder 4 Misfire?

Hello all,

I have the truck listed above Silverado that is experiencing a rough idle and misfire. My mechanic buddy tried to troubleshoot the misfire but was unable to. We swapped out cylinder #4 coil pack with cylinder #1, same with wires and spark plug one at a time. Cleared the P0304 code. It is still showing P0304 #4 cylinder misfire. He sprayed some carburetor cleaner to make sure we didn't have a vacuum leak as well and he said it was good. Any other suggestions to try to troubleshoot or repair my issue? I have changed out all 8 spark plugs with new ones. I have read that next is probably a good idea to do a compression test on all the cylinders but I wanted to see if maybe we are missing anything before hand. Any suggestions would be greatly appreciated. Sorry forgot to say we did swap the #4 fuel injector with #1 and still did not change the misfire from cylinder #4 to cylinder #1.