Physically, the transmission will bolt in. But, electrically, software wise, they are different. And Justin is correct, the 4T60-E is non HD vs the HD version in the 2001 GTP.
You are better off scrapping the 96 to get a new trans for the 2001. The bad thing about the 96 is, HP Tuners won't touch that year. They only support 1997 and up. (should you decide to tune it)