http://www.powerofbowser.com/index.htm
The dealer has a toll free number in the top right corner of the homepage - you can call them yourself. Just go through the menu to get to the GM Parts department.
Another reason I went with the HEN/HER - I figured that way I have a 2/3 chance of being correct instead of 1/3 for the CRD.
Depending on how hard it is to drop your tank - you could remove the straps and drop the tank enough to see the wiring harness. You should not have to remove anything - then just put it back together and order the correct parts. That is really the only way to be 100% sure.
I also considered ordering both units and sending the one I didn't need back - that is an extreme, but still an option.