What year/spec 727?

Continuing the case with this transmission, it is now placed in hot rod, and it is acting a little weird. It drives ok, but won't drive/reverse in idle, needs revs to start moving. Otherwise I don't feel any slipping, feels firm. Could it just be, that motorhome transmission/converter will act like this in a small car?
the motorhome convertor would be a low stall. all 727 have the same gear ratio. do i dare ask if you got the convertor into the pump all the way during the install?