All the testing I've done over the years, my cars have always liked to trap 300 RPM's over the best shift point.
I shifted my 340 Scamp at 6700, trapped at 7000.
Shifted my 451 DartSport at 6300, trapped at 6600.
69 Dart 500" shifted at 6600, trapped at 6900.

1970 Challenger, all aluminum 528 Hemi, HDK suspension, Tremec 5 speed manual