Well, I found out that if you remove the OD servo piston assembly, you need to insure that the band is aligned properly before putting it back in. If you don't, the piston tip may not engage the band, and your 3-4 shift will be more like a 3-N shift. (Of course I shouldn't have taken that assembly apart in the first place.)

I owe my local trans shop breakfast or summat for helping me to diagnose and repair my own screw-up. Of course you know who'll get my business if I end up needing a pro!

Thought I'd post in case anyone has trouble in the future.

Andy