I think I answered my own question. It's only 8 degrees F outside and snowing, so I was reluctant to do any testing. I forced myself to go out and check the relay. I have power at the 12v constant post. I turned the key on, and had 11.5v at the constant, and no power at the other large post (output). Checking the smaller ones, I had 11.5v at one, and nothing at the other. I kept checking all the posts until I heard and felt a noticeable click from the relay. After the click, I still had the constant, but nothing else. At this point I went inside for a while and warmed my hands.
I read a post on another forum about testing the relay, and it said with the 2 small signal wires removed from the relay, they should both have 8v. I came back out, removed the small wires, and tested them. I turned the key on, and one had 11.5v, the other had none. I still had the 11.5v at the constant, and of course nothing on the other large post. It seems to me that for the relay to operate, one small wire should have voltage and the other should have a ground. I understand that one is a voltage signal from the PCM, the other is a PCM created (controlled) ground. I don't really understand why they would both have 8v, so I think I got some bad info there. As I recall, the red one had power, the orange had none. I put them back on the relay, then went inside for a hand re-warm.
I came back out, and turned the ignition back on. I tested voltage again, and this time had 11.5v on both large posts, and one of the small posts. For some reason I think I was reading 11.5v at the ORANGE wire and nothing on the red, but I may be mistaken. It was freezing and I was rushing. I tested each post multiple times. I then switched to resistance and tested the signal wires. I think I got infinite on the red and no resistance on the orange, but again I may be mistaken. I switched back to voltage, and still had power at both large posts. I decided to try to start the truck since the relay was activated, and it started immediately.
I do have the block heater plugged in, which makes a difference. But, usually when it's "cold" out, the water temp is either half-way from the very bottom to the bottom of the "normal" range, or at the bottom of the normal range. Since it's only 8 out, the temp was all the way down, and not reading anything.
So, I do believe that the GPR is only intermittently making contact. I'm confused about the signals from the PCM, but they seem to be correct from what I can figure. I have to wait til the weekend, but I'm going to get a NAPA GPR109, and see if that solves my problem.
I wanted to re-test my glow plugs, but it was just too freakin cold for me. I may go back out a little later and check
2000 F250 Super Duty, 4x4, 7.3, 6 speed manual, 4" straight exhaust, 6637 air filter, superwinch hub locks, zoodad, foil delete, AIH delete, power pedal, autometer gauges, 2.5" leveling kit, 260,000