I had this same problem. Purchased a 318 CID 1972 Plymouth Satellite Sebring Plus. The previous owner told me the transmission was slipping (drivetrain was out of car). I had the tranny rebuilt-no problem. The funny thing is the previous owner also told me the slipping transmission was causing the points to "burn up" and that while driving the vehicle with the slipping transmission he was replacing the points frequently. His ignition problem explanation made no sense to me at all.

Now when I re-installed the motor and transmission, I was sitting in the patio installing new points only to find they would not even open at any adjustment. I had to purchase a new (made in Taiwan) distributor at Pep Boys. This solved the problem for awhile. But then I noticed a missing problem on the highway and it seemed the problem was the points again. I changed them out during a road trip and then made it to a motel where a waiting for Summit to rush me overnight a Petronix billet pointless distributor. No problems so far with that.

The points problem remains a bit of a mystery. I assumed the factory distributor was just worn, but why the new (not rebuilt) Pep Boys distributor starting acting up I don't know. Could it be a problem with that bronze/brsss distributor shaft bushing in the block? Don't know.