upper rpm break up

What do the spark plugs look like at the end of the run?
I had a miss at high load and high rpm and swapping the HEI ignition over to a MDS box 100% fixed it. I would not be surprised if the MSD box was warm, but I don’t think it should be hot at the end of a 1/4 mile run.
Maybe go over the MSD wiring and make sure all the connections are solid. Look close for heat affected wiring, that would lead you to the issue.