Yup, Agree - caliper slide pins are a very good spot to look - Ditto on checking the trailer brakes as well.

Brake pad wear - inner vs outer pad, front vs rear & left vs right side is another thing to check. Does it feel like the front end is bouncing up/down? This simptom = stuck or sticky Caliper pins nearly 100% of the time. This can be misinterpreted as an issue w/ the ABS system or rotors by some Dealer Techs.

To me it sounds like this problem may be a combo effect of several things - trailer brakes, caliper pins, brake pads and/or maybe a slow/sticky caliper. Does this truck ever pull to one side on some but not all hard stops? = Sticky Caliper.

DG