Mine goes out in the same spots every day, and some new ones every year. Basically, any season the trees have leaf-on conditions, the signal is getting denied by these thin vascular plants. I can drive down the interstate beside a mountain and it will go out, or sometimes start faintly playing another station simultaneously in the background combined with some static. Driving down a country road, signal will fail longer than it works for the most part, unless there is not any canopy covering the road. I also had it go out once and never come back on until the truck was turned off and on.
I don't blame any of it on GM though.
I have not had the best reception with sirius or xm radios throughout our state for years, not just GM vehicles and both aftermarket and oem radios alike. I think I got the best signal when you had to buy an actual sirius or xm radio to add in your car, before the service came built into them. Those worked in the house and in the car just as well. I've just grown to accept that the satellite signal is sh** in the West Virginia hills.