Firmer 1-2 shift?

Like green said you can try adjusting the throttle pressure and see what happens. If it's not maxed out already it'll shift firmer. If it is maxed out already the only thing I'd do is remove the springs(s) on the 1-2 accumulator (lower middle part of the first pic in 73's post) and put a blocker rod made from a 2-7/8" long piece of 1/8" water pipe underneath it. If you do any more than that it could be detrimental (it could create a shift overlap situation which is real bad) due to the design of the rear servo. Blocking the accumulator will firm up the 1-2 shift a pretty fair amount.