Gates was/is the GM supplier for the 12580196 A/C Belt Tensioner and also to AC Delco as P/N 38159. It fits all four years of the SSR, both 5.3 and 6.0 liter applications.
Part Number Cross-reference:
GM 12580196
AC Delco 38159
Gates 38159
Please note that your tensioner may come with either Gates or AC Delco packaging.