727 B&M shift kit problem

The throttle pressure adjustment can affect the shift alot so you might try cranking it down some more and see what happens. BTW: When you discarded the spring in the accumulator did you install a blocker rod to keep the piston from moving? If not that's a potential problem. I always block them with a rod (sometimes they come with the kit and sometimes you have to make one) mainly because I don't want the piston to bang hard when pressure is applied. Not positive it would cause the delay in front band engagement but it's possible.