If you have rear drum brakes, which I know some of the new heavy duty models still do, I may have a possible solution.
I had the same exact symptoms on my 2nd generation ram after replacing the rear brake shoes. Anytime you get new shoes its sort of up to you, or in your case the dealer or factory, to set the initial gap adjustment between rotor and shoe surfaces. This is done by adjusting a gear like screw that either pulls in or pushes out the shoes. Then the automatic adjuster takes it from there and expands over time as breaks wear down. But Too big of gap at first and the brakes don't grip the rotor surface tight enough,, and too tight and you won't be able to get the rotor slid back on over the shoes. A happy medium is good, BUT EVENNESS of spacing between the two sides of your truck is most important. If the left side is tighter than the right, the left will grip first and grip hard, causing a sharp pull to the left, or vise versa.
New trucks have new shoes, so this is a definite possibility. Of course .... Over a long enough period of time the wear of the shoe and the compensation of the auto adjuster should eventually even it out somewhat .