Most owners of the first year 1999 S80 T6 have problems. After 2001 I dont see or read the complaints as much. I own a 1999 S80 T6. I bought it used and a week later had to have the throttle body cleaned, new mass air flow sensor installed and the transmisson ecu reprogrammed with a software update. Most of the tranny issues are on the 99 models. I also had the shift silenoid replaced on the tranny. Volvo uses GM's 4T65E with a front limited slip differential. The tranny can be made very reliable and its very strong too. My advise is to purchase and aftermarket performance ECU it solved all my problems and has on every person I ever talked to that purchased one. Ive owned 3 Volvos and all of them were plagued with mechanical issues. But Ive never rode in a big sedan that rode as smooth as the S80. It also performs really good.