I'm suspecting glow plug relay troubles here, but I've never experienced it quite like this:
.
1. Key on, Wait To Start Light goes out, try to start truck, no start.
.
Ok, I figure it's a cool morning, give the GPR a few more secs.
.
2. Key on, WTS light goes out, wait additional 30 secs, crank, no start.

Hmmmmmm.....
.
3. Key on, WTS out, start countdown for additional MINUTE, and at about 40 seconds, I hear a loud "CLICK", a pop, a puff of white smoke! I crank, it starts, pumps white smoke for about 10 seconds and smoothes out.
.
So.... was that "click" the GPR "finally" kicking on, or something? We have 6 of these trucks, and never seen that happen that way, but it has happened to this truck two mornings in a row last week and again this week.
I guess the next thing for me to do is wait for it to get cold again and check the GPR Pass side term for voltage at key-on, eh?

the click was probably when it went off. when the truck is cold, eot temp below 80 degrees, get someone to switch the truck on while you monitor the relay with a test light. KOEO both sides of the big posts should be hot. now, the relay will still click even if the load never passes through it. if you have power going through the relay, you might need to ohm out the glowplugs through the uvc harness connector, 1 ohm and no more.

found anything out yet?

I ohmed out all the Glow Plugs... within normal limits. The GPR had 13.5 in, and 12 out... but the kicker was the resistance across the GPR was way off. I've ordered a new stancor unit for it and it should be here tuesday, I hope.

kool great job. need any help let me know.

MrFixIt
I've read plenty about GPs and GPRs and finally decided that I would simply unplug my GPR for the spring thru fall. You know, that little plug that controls it, right next to it....
Since it's been warm, I decided that it couldn't hurt to see what happens. I crank it now for about 5 seconds and it fires, so I musta not done nothin wrong.
I'd had trouble starting the truck in winter so I changed batteries, which helped some. Then I checked the harnesses and found a burned connector. I decided to check current draw for the GPs and found that only 2 of them worked !
Changed gaskets, plugs and repaired the harness outside the cover. Then it started normally the rest of the winter.

So I'm just wondering if the GPR is of any consequence when it's warm.

But I think your choice of the Stancor is a wise one.

BTW
to check the relay, turn the key on and put the colt meter across the big terminals of the GPR. This will measure the voltage drop across the relay when it's working. If you get more than several tenths of a volt, you might just have a flakey relay. If it's a volt or more, GET A NEW ONE bcuz the contacts are burned/pitted.
RoGrrr