727 help

What rear end does it have. Last 3 digits will determine if it has a crush sleeve. As said, I don't think that's your issue.Your kickdown linkage adjustment might have changed? It regulates pressure for your shifts. You could turn the linkage adjuster in (shorter) a few turns and see if that helps. That's up by your intake manifold. Just remember where you started so you can put it back if it's not the issue.
There is also a screw at the tranny that regulates your pressure. That's another can of worms I wouldn't touch that until I was absolutely sure what the factory setting is.
Just wondering if those were touched when doing the work you did.