i have recently started driving my 1975 c20 with a 454 and th400. if i put the trans in Drive it starts in 3rd and goes really slow from a stop. i can shift it manually through all the gears but it will not shift automatically, the kickdown does not work and and the vacuum modulator does not suck ATF. i checked the governor and the gear was not stripped and the weights move, all seems to be OK except that it wont shift automatically. ATF levels are fine ANY SUGGESTIONS?