That's always a fun project Tim.......not lol
Sounds like you have a later model governor in there that shifts at 4000. My 79 454 pickup was the same way.
It's a long exercise to play with those things and get them exactly perfect. No additional advice that hasn't already been given other than have patients and enjoy taking that governor in and out a dozen times and hot fluid running down your arm pits.
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2019 Pontiac Heaven class winner
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