Well, I figured out most of my problem...
My starter was fubar. Whoever installed it cross-threaded one of the bolts. A buddy noticed it throwing sparks when I tried to start it yesterday (at 10 degrees). I had cycled the glow plugs TEN times before I started trying to start it, then 5 times before the 2nd try, then 5 more before the 3rd try. After that, I quit because it started to die on me.
My buddy hooked up a generator to it this morning and plugged the block heater in for a few hours (3-4) and a battery charger to top the batteries off (they were down to about 7 or 8 volts from the cranking the day before). After about 3-4 hours of heating/charging, he gave up. Took the starter to Auto Zone to confirm the fubar condition and picked up a new (reman) one.
Put it in and it is starting like a champ now. It's like 20 degrees out now (maybe lower, I'm not sure) and it fired up for me like nothing.