Gates was/is the GM supplier for the 12669569 Main Serpentine Belt Idler Pulley and also to AC Delco as P/N 36299. It fits all four years of the SSR, both 5.3 and 6.0 liter applications.
Part Number Cross-reference:
AC Delco 36299
Please note that your idler pulley may come with either Gates or AC Delco packaging.