what did the kit instructions tell you to adjust the bands to ? using specs for a 66 to adjust a modified 77 isn't a good way to go , also that 2.9 lever might be part of the problem , that ratio will apply the band way too fast , you should have at least a 3.8 , preferably a 4.2 .

also you having to replace the rear drum ??? sounds like that trans may have had an issue before ?

contact member randy J and buy his billet servos , you are going to blow out that rear servo eventually with the higher pressures and the heavier spring from that kit .