I didn't read all the posts on this but many many years ago when I had a 727 three speed shifter I had to totally have my hand off the shifter and bang the shifter for each shift. If I had the slightest pressure on it the detent wouldn't work and it would go from 1st to 3rd resulting in a loss of .10

1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27

Livin and lovin life one day at a time