95 Dodge 1500 318 Stalls

About a month ago, driving at steady highway speed, level terrain, truck goes thump, like a hard shift, then runs normally. This happened a couple of times then one morning the engine died completely. I pulled over, stopped, and the engine restarted immediately with no further problem. Next time I restarted without stopping. This morning it died and would not start for several minutes. Then it started and ran normally. Today the water can light was on while it wouldn’t start. No codes displayed except 12, 37, 41 (“battery disconnected” from a dead battery a month ago) which are always shown. Always occurs at highway speed, normal engine temp at 200. I filled the fuel tank last week and this morning it was almost full. Engine has about 80,000 miles one it. Any ideas would be appreciated.