Ugh. Here I was having a good evening and then you went and cussed!Dorman
Adding to your part numbers, here is the diagram for the left and right pieces. It’s strange that a parts store couldn’t find the part. Then again…
Also, here is the spring part number. Looks like they sold it with a hardware kit but two kit part numbers show up that match a 99 Yukon [model 107(06)] and both show it as right rear. It wouldn’t matter if it includes springs for both sides, but that may be the source of confusion at the parts counter.