What is the exact transmission? Lockup or Non Lockup? If lockup is it a Hyd. applied or release? Reason I point all this out is that it might be a valve body/lockup circuit problem also.
Yep, it would do exactly the same thing if it was an activated lockup converter.
Actually have seen that happen, and I can't remember which one it was (thinking 700R4?) that would sometimes not unlock when coming to a stop because of a stuck converter piston.
I'd be surprised if after all this he mentioned it was a lockup though.