Concensus re: which year(s) are more reliable?

[dcarlson12]

Probably has been discussed to a certain extent but please chime in with opinions about which year(s) are more reliable.
For example it seems 1999 to 2001 seem to be considered worst.
Is this based upon mainly the transmission failures?
I believe the same transmission is used from 1999 to 2005 at which point I don't know what tranny is used at least for the T6.
Did Volvo realize that the tranny was weak and used upgraded components in later years or ???
I know the T6 is considered less reliable mainly based upon the fact that the tranny can't/couldn't handle it....