So the problem appears to have fixed itself. I was playing with timing, advancing and retarding it to the point of being extreme, and and the truck let out a nasty little backfire and blew a rather large hole in the muffler (there were little peices of muffler laying on the garage floor). As it turns out, the problem completely went away with the giant gash in the muffler. I re-tweaked the timing and took a peek inside the muffler to find layers of rust flakes inside it. I'm sure it was badly clogged. Looks like I was having a back-pressure problem all this time. At least I can drive it now without the stuttering, even if it is a bit on the loud side.
