Cylinder two misfire

My truck listed above has a bad miss on cylinder number two. I've already tested the plug, wire, coil pack, and injector, all are working correctly with good connections, and the computer is sending signals correctly with no skips, also ground connections are all good. I ran a compression test on cylinders two and four to see how they lined up, both hit about 180. However, I will mention that the number two cylinder seemed to take much longer to get to 180, every hit it would go up some, but half of the time it would go down 10-20 psi after it had just gone up, but eventually made it to 180. Cylinder four on the other hand had no issues getting to 180, and every compression stroke always resulted in positive psi.

Something else I should mention I just recently noticed a tapping in the block somewhere, but only when the engine is completely warmed up, its definitely not a rod know or detonation knock, it sounds more like a lifter. The noise does fallow engine speed, I'm thinking it could be the exhaust valve for that cylinder getting stuck, but a second opinion would be greatly appreciated before I start taking the heads off.