I was in the US a few months ago and did experience what you are talking about on the interstates, so I get where you are coming from. It was actually kind of a strange experience to be out of service so often.

But here in Canada, where I spent almost all my time, the only place I've ever had any significant coverage issues is when I was in the far north, and I've only been there once. It's essentially a non-issue for me.