I don't think the tranny work had much to do with it, especially the odometer.
On the slight possibility that the ring gear on the output shaft somehow became slightly eccentric
that MIGHT account for the bouncing gently, although my guess is a cable problem.
IF the speedometer works at all, the odometer should work because it is geared directly to it.
Therefore the odometer problem has to be inside the speedometer housing; a broken gear
or one that stands still on a rotating shaft.
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George Downs, Bartlesville, Heart of the USA!