727 tech question.

I have a 727 non-lockup with a reverse shift/manual valve body. Also has a TCI 8" converter. Just got the converter back from the shop having it adjusted to 3000 to 3500 stall. Before removing the converter the transmission would stall the motor or at least pull it down 500 to 700rpms when shifting into gear. First thought for me was converter was messed up. The torque converter shop guarantee that the converter is fine. Question I have is, have any of you fellows ever seen this issue before and could it be caused by internal components in the transmission, possibly the valve body? Thanks for your assistance.