Automantic Tranmission Shifting

I have a 400 Auto trans. in a 1968 Chevy C-10 pick-up with a 327. The frist shif, from 1st to 2nd is around 10 to 15 miles an hour. 2nd shif, from 2nd to 3rd about 25 miles an hour. I would like the 1st shif to come in at 20 miles an hour and the 2nd shif about 30 miles an hour. There is no ajustments with the leckage. So many thing have been change and removed. I know on a powerglide you can change the shif by srewing in and out on the srew in the mos. vale at trans. Is there a simple way I could change the shifting, Or would I have to do a few things with the leckage or somthing else? Thamks John.

I'm not a GM guy, but I think you have a vacuum modulater adjustment that would do the trick. Somebody will chime in here before to long. I think there was even a thread on this topic a while back, too. You might try doing a search and see if that turns up anything.

Summit has an adjustable modulater for twelve bucks.