At 10K hours, pretty good chance your intake valves are carboned up and not seating. Pretty common issue on my high hour trucks. Generally doesn't reveal itself unless the truck has been sitting and the carbon hardens up. A shot of compressed air through the spark plug hole with the cylinder on the compression stroke will confirm this with leakage back through the intake.

The right way to fix it is to pull the head and replace with a reconditioned one.

There are a couple of tricks to try to get it to seat, but I'd have to write a long disclaimer before I'd publish them.