About 500 miles ago my tranny started to shift like an old muscle car with a shift kit. Shift timing is as it always was but it is crisp to the point of being annoying. There is no flaring or other discernable bad habit to note.

This happened all of a sudden so I'm thinking it's a vacuum issue. The hose from the intake manifold to the vacuum modulator on the tranny was replaced to account for a possible failure there but nothing changed. I moved on to adjusting the modulator to soften shifts but the little key turns as if it is acting on nothing. I can turn it in either direction any number of turns and it has zero effect on shift quality. On top of that, the key will no longer settle back into the crowned recesses before replacing the rubber cap.

I'm thinking the diaphragm has expired allowing something to occupy the last little bit space that the key nestles into. Any thoughts on this issue? Can the modulator easily be replaced?

The car has 256k miles and has always run like a sewing machine. I literally grew up with it as it was my mothers car so I know it like the back of my hand. This will be the first work the car has required outside of scheduled maintenance in its entire life. I feel as if it may finally be broken in

Sam