Electrical question - Truck dies while driving

[kxmotox247]

I am fully aware that this truck needs to be rewired. However, I can't afford that right now and need to find out what the problem is. I am stumped.
My 67' always fires right up. The problem only seems to happen once it's warmed up and is very inconsistant.
I can drive at 35mph or 65mph and the truck will die, make backfires (that sound like gunshots and scares the hell out of my girlfriend), the radio dies, the tach will go all the way around completely clockwise. Sometimes the truck will pick itself back up and keep running. Other times, it won't. So as soon as I feel the truck fall on it's face...I'll throw it into neutral and turn the key off.
It's got an HEI distributor. I thought maybe it was the ignition module so I grabbed one out of another old distributor. I noticed that the one in the truck didn't have any grease on it and pops said that it should...it needs the grease to actually held transfer heat out of it and into the dist. instead of cooking itself.
Anyway, the truck still has the same problem. It just seems to lose all electrical power. Sometimes it will come back on it's own, sometimes not. It always restarts. But it's definately taking the reliability/dependability away from driving the truck.
What's going on? Any ideas? Another bad ign. module? Bad Battery? Bad Ground? Ignition switch power problem?
Thanks!