Intermittent stalling

[slow72]

**I've also posted this in the electrical section i just thought it would get more traffic here. Move/delete if necessary.

For starters i've got a 72 GMC with a 250 in it. The PO added an HEI distributor and did away with the resistor wire for the points setup. The problem i'm having is the truck starts and runs fine, then after a few minutes of running the idle becomes very choppy and then it eventually stalls. It will restart after a few minutes but acts the same way.

I've replaced the module and it didn't help at all. However when checking for power at the distributor when it was running i was only getting 6 volts and when it begins to run rough it bounces between 6 and 0 until finally stalling at 0 volts. The power wire runs from the distributor to the ignition terminal on the solenoid. With the engine not running i get 12 volts at the ignition terminal and at the distributor. But when running, only 6 volts.

What's going on!? Thanks in advance!