According to the factory lit. our cars weigh 3650lbs.
The 4T80 was used in the Bonneville because it is an H body which is similar to the K body of the old Seville and Deville, which is now the DTS, and because the Northstar was already mounted to the 4T80 in those cars. I'm guessing it got the Northstar/4T80 combo because of the similarity. I've read that the 4T80 is specific to the Northstar. I'm guessing that it is not as easy to put a different transmission in a front driver as it is a rear driver, and so they just kept the 4T65HD for our cars, even though the LS4 was a new engine and could have been adapted to the 4T80. All of the W bodies have 4T60s, 4T60HDs, 4T65s, or 4T65HDs, depending on their year and engine. The HDs are just for the supercharged 3800s and the LS4s. The 3800 Bonnevilles had 60s and 65s.
I've checked a couple posts/comments about the 4T80s, and I don't think that they are by any means perfect. I've also heard that they cost more and weigh more than the 4T65s. I'm just guessing, but I think you would be talking similar $$$ to seriously beef up the 4T65 or to beef up and adapt a 4T80.
