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, Ford and General Motors -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.