Interesting. I just went to GMPartsDirect.com, and they don't have 84034699 listed. But they do have 23315255 on sale for $279.35 plus shipping.I ordered from GMpartsdirect.com. They, too told me that 84034699 superseded the other part number(s), which I originally ordered.
Total for me was $365.05 which includes shipping. It' supposed to be shipped to me sometime next week. I'll report back to the group when it arrives.
Am thinking of just buying 23315255 and seeing what happens from there.