I carefully followed Greg's advice with my Hydra-Matic and it would shift from 1st to 2nd at about 7 mph and also shift fine into higher gears (and down-shift quite nicely, too - when slowing down and when making a full-throttle forced down-shift). I think I was just lucky.

http://chevy.oldcarmanualproject.com/booklets/5430sm15.html