As far as the leak down is concerned.. There are a couple of ways to check to see where the problem exists.. All involve listening for air leaks/hiss.
1. Open oil filler cap with pressure applied, listen to hear if leaking into crank case, will be somewhat hard to determine, put ear next to filler tube and put hand over and release quickly. If you hear AIR here, that means its either the RINGS or a HOLE in a piston
2. Stick your ear next to the exhaust with air applied, yep at back of truck. This will be easier to hear than #1 if its leaking.. This will indicate a bent/worn exhaust valve or one thats NOT seating.
3. This one is a little tougher than #2, find some way to locate near the intake manifold/IC and open it up to listen for air leaking there.. That will indicate a bent/worn intake valve or one thats NOT seating.
4. This test has a 50/50 chance of working (sometimes it does, sometimes it doesn't) Open the RAD CAP with pressure applied (cold engine) and watch for bubbles.. IF you see bubbles its a good indication that its the head gaskets...
Also, FWIW, we do this kind of leak check ALL the time in the aviation world (piston powered airplanes) and its almost a required item. All I can say is, make absolutely sure that its at TDC with BOTH valves closed, even the slightest will cause erroneous readings.
Lastly, if you can get the truck started and you are at the point of NO RETURN start the truck, let it warm up to idle and get everything GOOD and warm, its quite possible that some of the readings will reduce a fair amount.
Oooops, lastly again (sorry forgot this) try squirting a little OIL on top of the piston you find the leaks on.. This will temporarily seal a WORN set of rings (unless they are missing)... Use a HEAVY OIL and dont over do it (dont wanna hydro-lock the motor).
Have I forgotten anything ???? Anyone ???? Feel free to chime in (like I can stop ya :wink: )