Well, I gave the radiator a good soak with white vinegar. It seems to have helped quite a bit. The only real test will be getting it out in some serious traffic or on the interstate.
For those not following my previous overheating thread, the temp gauge was exceeding 210=B0 (12 o'clock, or directly in the center of the gauge). When I'd slow down in the stop-and-go traffic of Atlanta, the truck couldn't dissipate the heat, so when I'd take off again, it'd continue heating up. It was compounding and just kept getting hotter. The only way I could keep it out of the danger zone was to run with the heat on--not exactly fun in 95=B0 weather.
I first connected a garden hose to the side of the heater box that returns to the radiator. Then I flushed the whole system till it ran clean. Then I removed the radiator, and after flushing it with clean water, I capped it off completely, and filled it with White Distilled Vinegar. I let it sit for about 3 hours, then drained it, flushed it with water again, re-capped, and refilled it with vinegar. I drained and flushed again after 3 hours.
I then filled it with vinegar a 3rd time and let it sit overnight. This morning after a good flushing I reinstalled it with new hoses, and ran a hose straight from the intake manifold to the radiator, eliminating the heater core. (hopefully to improve the performance of the A/C).
I took it out for a spin a few minutes ago, and it was better. In fact, after trying some Prestone radiator flushing product (waste of time if you ask me) I took it out on a cool night, and it still ran hot. Today, it's 93=B0 outside, and it did NOT overheat after the vinegar treatment. I even tried to make it overheat by running up steeper grades while keeping the carb out of power mode (richer) and it would not get up to 210=B0. I don't know what temperature "normal" is, but it's around the 1/3 mark on the gauge, 1/2-way being 210=B0.
Thanks to SnoMan for the vinegar suggestion and all the others who've helped. I'll be installing an auxillary electric fan, maybe one of those neat dual-fan setups, as time and money permit.
Thanks again,
~jp