Scotty,
I've got Sirius in 3 vehicles so here's the dope. The receiver should just about NEVER loose the signal unless: Traveling in a tunnel or under a large overpass may temporary block the signal. Traveling on a below ground level roadway bordered by tall buildings [Cross Bronx Expressway] lower Deck of a Bridge [George Washington Bridge in NYC], The antenna is not mounted clear of obstructions on the vehicle, it belongs out on the body of the car at least 18" from any pillars, spoilers or fins! Yer in Tejas so as long as you have an unobstructed line to the north from the antenna the signal should not be blocked. I've got 1 place here in Feenix that cuts the signal for a second or two.
rich