woody: your story illustrates how your truck would benefit from aerodynamic mods (aero shell! partial grille block) much more than a non-cylinder-cutout version, since you'd be able to enter 4-cyl mode sooner, and hold it longer. (Assuming it's a load-dependant thing.)
And it suggests that a 4-cyl truck would be even better than a 6- or 8-cyl one.
(Ducks for cover!)