Gates was/is the GM supplier for the 12587562 Main Accessory Serpentine Belt and also to AC Delco as P/N 6K938. This fits the last two years of the SSR, 6.0 liter applications only.
Part Number Cross-reference:
GM 12587562
AC Delco 6K938
Gates K060938
Please note that your belt may come with either Gates or AC Delco packaging.