[DL60]

hi guys im starting to restore my first big pontiac i bought a 60 ventura 389 a.t. i got the car up and running after a lot of tinkering i was hoping to get the engine and tranny straighten out before i started the resto.i have been driving the car for about a week now and the problem im having is when the car shifts from 1st to 2nd it slips i can manually shift the car from 1st to 2nd and it doesn't slip. i was wondering if a filter change might help?? i have to admit i know nothing about the tranny other than i have been told its a slim jim. i have checked around my local parts stores and cant find anything about these trannys let alone a filter i just get a blank look from the people behind the counter so any help and info you guys could give me on this tranny would be a great help like is there a model number for this tranny,anywhere i might find a filter,and guess to what my problem might be with the slipping,if all fails is there any way a newer model tranny can be adapted to a 60 389.thanks for your time&help.