727 won’t upshift 1-2 or 2-3 without lifting throttle?

Hi!
Been working fine 1.5 years ( except for 2-3 flareup below) and out of the blue I went to return home after 1 hour cool down and it wouldn't upshift (1-2 & 2-3) until I lifted throttle.
Linkage & throttle lever shaft function looks correct.
Fluid level good. First & reverse fine.
history: 40k mi on rebuild 35 years ago.
Transgo shift kit 1.5 year/5k miles ago. never got rid of a (mild) 2-3 flareup subsequent to kit install.
I plan on going over the linkage adjustment again, then dropping pan to take a look see.

Any ideas?

thanks
Author: droptail