Starters pull fewer amps when hot, and as a result crank with less power. The charging system has nothing to do with starting, charging problems and starting problems are 2 separate problems. Though a bad charging system can lead to a drained battery which will affect starting.
You need to look at alternator, voltage regulator or charging system wiring.
Who cares how much horsepower it has, all that matters is how fast it goes!
Untested 331, lots of suspension, chewing up corners.