I think your odometer may have one of two problems.

The common one written about is a cracked nylon gear. It loses its grip on the shaft.

The one trouble I had on a high mileage 84 was under the die cast gear; the shaft had worn thin.

Both troubles tend to exhibit themselves as things warm up and expand, I guess.


--
Art Benstein near Baltimore

A husband got in big trouble after his wedding anniversary.
His wife told him the day before: "Tomorrow there better be something in the driveway for me that goes zero to 200 in 2 seconds flat."
The next morning the wife found a small package in the driveway.
She opened it and found a brand new bathroom scale.