The pump is what the torque converter connects to. the case of the converter spins which spins the pump. If you pull the tranny and remove the converter there is a cover that you can remove and the pump is behind that it has an oring around it that seals it to the case. That ring could have gone bad or the vanes in the pump could have gone out. The only real way to tell is to pull the tranny and check it out. First thing I would do is to drop the pan and see if you find anything abnormal in there.
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