How does your tranny shift ?

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I hate the way my TH400 shifts. I suspect it has a problem with the vacuum modulator, but I know very little about trannys, so I thought I'd check with the pros here on the BB.

First gear shifts almost instantly, even under WOT. Under part throttle the 1 - 2 shift will happen at like 10-15 mph.

The 2 - 3 shift comes up by 30mph. Downshifts are hard to come by and then the shift back to third is too fast for it to do any good.

Manifold vacuum is good. 18 -19 inches if my gauge is right. I've had the downshift solenoid replaced and fluid/filter change within the last two years.

Any suggestions?

David