1) Replace both front brake hoses. They deteriorate on the inside, I have no idea how that would show up on any kind of inspection short of removing them to look inside. At that point why would you put 13 year old hoses back on?

2) If its been an issue since the truck was new, I would shorten the adjustable rod between the master and the booster by about 1/4 turn. Its possible the adjustment does not provide enough clearance and the under hood heat is expanding things just enough the brakes are always dragging when everything gets hot. When you adjust it by shortening the rod length, you are effectively giving the brake pedal more free travel before it actuates the brakes. Understand, a little adjustment goes a long way, the adjusting bolt is a fine thread bolt, but a 1/4 turn is a lot of movement. You may also have to adjust the brake light switch after so the brake lights don't stay on, but usually the rod adjustment doesn't effect the brake light switch adjustment.

3) It is possible the brake light switch is out of adjustment and may not be applying the pedal to fully return to its designed position and is still holding pressure on the brake pedal. This one is a long reach, but I have seen it before.