Hate to go in a completely different direction. But, did the tach and the stalling happen at the same time? Could the tach have shorted something in the ign system causing a very weak spark? Just throwing out ideas at this point.
Nope, I had my negative batter cable fall out of the terminal because some old guy messed with it when I helped him on the side of the road. He thought he was tightening it to the battery but he was actually loosening the wire from the terminal.