Did u flush your converter and get all the old fluid and clutch material out of it?
Also, maybe you didnt torque the pump properly? I never rebuilt one, but my memory tells me that someone who did this had a similar problem, and the pump that is in the front of the case wasnt installed corectly. He pulled it apart again, retightend the pump bolts, and all was well.
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1993 GT/AOD
'93 Mustang GT