The 2/3 shift on a torqueflite has one issue that's hard to get around. You have to release the band and apply the high clutch to get the shift, because of that no matter what you do for a little space of time you have a clutch and a band partially applied. Band lever ratio, and adjustment as well as clutch pack clearance, number and kind of clutches all have to be juggled to get a good no flare 2/3 shift. I always look at the condition of the band and clutches to see which area I need to juggle to get it just right. If the band is dark, I tighten the band adjustment, or try a different lever ratio for example.

But the rest of your post describes what sounds like a converter issue.