I was able to spend some time on the truck this morning and found the root of my problem. The buss bar on the left (driver's) side of the engine was rusted through between the #1 and #2 glow plugs (the two closest to the firewall). That's why it acted like none of the glow plugs were working. Only 1 of 8 was getting power.

I tested all 8 glow plugs and #1 (left side, closest to firewall) was bad. I'm not sure if it's coincidental that the only one getting voltage was also the only dead plug. I find it strange that the computer didn't set off the SES or set a DTC. I also checked to see that I was getting voltage from the controller at key on and it is, so I believe that a new glow plug and new buss bars (I'll replace both while I'm at it) and I'll be back in business.

I was able to pick up a glow plug locally and managed to replace it without snapping the original off. I soaked it for quite a while with PB Blaster and it came out pretty easy. I have to wait on buss bars since the local dealer is out and my wife is picking up a set from the dealer in the city where she works.