~ Two Things ~

I had an 88 Ramcharger back in the day that had similar issues. After several days of troubleshooting and parts replacement, it turned out to be a connector near the battery with corrosion. It was a large wire, with a bullet connector in it, and appeared to be sealed, but was not. After it was cut out, and soldered, the thing ran normally again.

The problem came on suddenly, too. It kicked and bucked and was rather violent, but was nearly impossible to find.