The folks who drive pickup trucks are an ardent, consistent lot. They stick to the brand they like more than those who own SUVs, minivans or any other type of vehicle. They are however human, and the heart wants the half-ton that it wants, as the saying goes.

This week at the North American International Auto Show in Detroit, each of Detroit's so-called Big 3—Fiat Chrysler Automobiles NV, Ford Motor Co. and General Motors Co.—is showing off a new pickup truck in the hopes of tempting customers currently wedded to a rival, or at the very least keeping its own drivers from straying. Pickups are immensely profitable, with each truck sold carrying about $10,000 in profit. With that kind of black ink at stake, auto executives have been questioning just how loyal the typical pickup truck owner truly is.

When it comes to full-size rigs, roughly half of pickup truck owners re-upped last year, trading in a full-size truck and buying another rig from the same brand, according to Edmunds.com. Another way to look at it? Some 50 percent of these drivers are ready for a fling, which means that in the $90 billion U.S. truck market, $45 billion is in play. 

And that estimate may be conservative. In a recent survey by digital marketplace Cargurus.com, 60 percent of truck owners said they would be open to switching brands. When price was factored in, that figure rose to 71 percent. In other words, there's a reason why Tesla, the ultimate left coast brand, is so popular in blood red Texas, where one in five U.S. pickups are bought. These truck customers are far more idiosyncratic—some would say irrational—than they seem.