2 speed power glide question

ok i have a leak in my tranny, and when i bought the car about a year ago the tranny seemed kinda weak. im gonna have it checked out and someone told me that it might be better to get a new tranny (th 400) instead of rebuilding the current one. or should i rebuild the powerglide then highperformance it.

A th350 would be a drop in swap. th400 if you have a lot of hp.
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