I also swapped to the painted antenna, and lost XM. My issue was that my 2014 Antenna only had the purple connector, and the new Painted Had the Same purple antenna, but also a gold connector. I believe that the XM antenna is the gold connector in the 15+ trucks, where it was in the purple Connector in 14.
I believe that its as simple as swapping the antenna switcher that is on the passenger side upper dash under the speaker trim, and XM cable, but I would like to get a thread together and see what part numbers are, as I don't have access to GM documents.