Hi folks:
I've a 79 KC and some long time ago I had exactly the same thing happen as you relate; driving along and the sucka just dies and no matter how much gas, it limps along, then works for a little bit and dies again. Luckily I knew a mechanic that knew his stuff. It was the little black ignition module near the distributor. It was "done" and had to be replaced, period. Once done, no further problems for another 100K miles and still going strong. The rub was that the part (new) cost nearly $300. It's because the module has a very small piece of platinum in it, and that stuff is worth much more than gold. I've still got that little piece of platinum becuase I asked for the old module when it was replaced.
Good luck.