I had the same issue in my 86 2+2. The shift point was like yours. I had changed the carb and wasn't able to get that cable to the tranny to work right, My tranny guy put a constant pressure valve body in. A TCI part available through Summit. The tranny shifts good but not what I consider optimum. The tranny now has over 15,000 miles on it. So the valve body has allowed the tranny to live.
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