Muzzleloader,
My guess would be a stuck valve also. I don't think it is your gauge, if it was it would show bad readings on more than just one cylinder. You say that the engine runs good, but it may not be as good as you think. I had a 350 in my C10 and it also ran good, or at least that is what I thought until it started giving me trouble. Did a complete engine check and found bad rings, burnt valves, plenty on "slop" in the timing chain and gears (don't know how it ever stayed in time) and oil pump screen was almost totally blocked with junk. I installed a new engine recently and I can't believe how I ever thought the old engine was ok. Just my 2 cents.
