I don't know if anyone can really answer this question, but a tranny rebuild doesn't change the "design" in any way, but rather just means replacing the parts that caused the failure and any others that were affected by those parts. No, a transmission shouldn't fail at 47k, but it happens occasionally on even the best designs..or even trannies built to be "heavy duty". In my experience both personally and by association, tranny rebuilds can be hit or miss. It may be fine and last the life of the car, and then again introducing new parts combined with those that are older and have wear could cause additional problems down the line...only time will give you your answer.