DB Electrics stuff actually has a pretty good reputation I thought.
While it might be the starter (did you call them and ask about it by the way?), it might also be the other things like gr8scott was saying.
What is your base timing set at, and how is your vacuum advance connected?
And what size and condition are your battery and starter cables? Even though the new starters take fewer amps to turn, an old tired, or undersized battery cable, or poor ground can have the same effect.
And speaking of which, where is your ground cable connected?
Guessing this was not a problem previously though? If not, then yeah, probably something with the starter.
Unfortunately though, these Broncos of ours just love to throw "coincidental problems" at us. We'll change one thing, and two others crap out at the same time!
Good luck.
Paul