Differences between 97-03 GP's and 04-08 GP's?

Does anyone know if the 04-08 GP's had a different transmission than the 97-03 GP's or what the differences are? Also, what is different between the 3800 Series II and Series III engines? I know the GT's are rated at 200hp on both, styles, and the GTP got a bump up to 260hp, but thats all I know for sure

The transaxles are similar between both generations. 4T65E. From 1997-1998 GT and SE models had the 4T60E. Of course all GTPs, Comp G have the heavy duty 4T65E-HD which has a beefier differential and passenger side axle shaft.