No tests have been done with the engine hot. The engine will not get hot and I think this is the real problem. Some how there must be coolant flowing through the engine and bypassing the thermostat, I can't explain it any other way. It seems like I have to address this problem before I can fix anything else. Can a head gasket leak cause low temps?
I did not do the compression tests, so I can't tell you exactly how those tests were done. They were done when I sent the truck to the mechanic he told me the results and I relayed them to you. He said they look normal, I believe him. But he thinks its a lower manifold gasket, I had already changed this and know its in good shape.
I did put a Delphi pump in, I think its ridiculous to pay $125 more for a pump but thats what I did. There were NO delphi pumps in a 50 mi radius for an extra $25. They are always $125 more. I'm still not convinced it was the right thing to do. The pressure is exactly the same as before. After 30 minutes of running the truck (pump is warm, engine is warm not hot) the pressure on the block is 60 psi with key on engine not running. 52 psi running engine, 58 psi at 2500 RPM. Bleed down is normal. Directly off the pump, 95 psi, maybe a little higher but I don't let it run long on this test. Remember this is with a new regulator, filter, pump.
I'm also pretty sure I'm losing coolant, but I've had the thermostat out several times and it could be that the engine hadn't burped when I checked it the first time. I do not see coolant leaking out of the engine.
I just don't believe this is some obscure problem, I actually expected that someone else would have dealt with this before and chimed in by now. But I really appreciate the help I've gotten so far.