take the gauge off of your compression gauge and hook an air source to it... make sure the valves are closed because you want to find out where the compression is going, idealy is the piston is at the bottom of the stroke, the air will push it there anyways... remove the radiator cap and look/listen for bubbles... remove the dip stick and listen for air.. remove the air intake, listen there and listen at the end of the tail pipe... if it comes out of the radiator, its a head gasket... if it comes out of the dip stick, rings or pistons... intake or exhaust pipe, its the corresponding valves... obviously it could be any combination of these... perform check on all cylinders and report back... that air is going to go somewheres...