Those early Hydra-Matics did not shift as smoothly as the modern ones especially if your car has the six engine!  The one I had in my 48 Pontiac eight was even quite harsh during the first shift but was smoother during the last 2 shifts!  I have a Hydra-matic shop manual which shows how to set bands etc but very complicated and you needed all the special tools to work on them!  Most likely after you have driven the car for a while and put some miles on the tranny it should improve!  Have you had the trans fluid drained and replaced?  That also might help! Bob.

my hydramatic shifts fine but it does have a harsh downshift into first when your slowing down to a stop sign or light.Upshifting seems better.One thing I do notice since my driveway has a bit of a slope to it is the tranny has a whiney sound to it when I park it on the slope and go to open the garage door.Alot noisier than when parked on level ground for sure.That being said I put a lot of miles on mine this summer and other than a small leak on the garage floor it has run perfectly.If it doesn't leak its not a powerglide i'm told.