Poor maintenance , what often comes with little use is what shortens the truck life.
My 1999 Powerstroke was pulling 30,000 lb rigs routinely, when empty 450 truck with fuel and driver was over 10,000lb.
On CA grades quite often I had to climb long miles on 3rd gear (6-sp manual) and gas pedal firmly on the floor.
Still sold the truck at 300,000 miles running perfectly.
Met commercial hauler who clocked over million miles on the same engine. He did not run it empty.