Correct P/N for an A/C compressor please?
 

I know we have some GM gurus on here. My A/C compressor is going out on my truck. I found it on GMparts direct but it's a bit higher than the rock auto prices, especially after shipping... but gmpartsdirect won't show me the P/N for it? And Rock auto has literally 20 choices, all look extremely similar to me... I want to get the right one.

The truck is a 2000 5.3L 4x4 ext cab 1500 silverado. VIN T.

Thanks.