AC2018

I just bought a new 2018 Denali and the XM reception is terrible. Some channels are clear, some muffled and some just drop. I have three other vehicles with XM and not one of these has the dead spots that I have in the Denali. It is in the same spots in the city and there are no overhead obstructions. I have had it two weeks and I thought maybe I had a bad antenna connection or something but after reading this post it appears it is a common issue. Has anyone resolved this with a fix? Thanks!