Truck life is not affected as much by hard work it is by lack of proper maintenance, overheating components in the drivetrain, and hauling/towing more weight that the truck was designed to tow or haul.
Especially with a diesel engine, you want to work it hard. Get it hotter than a two dollar pistol at least every few weeks, by towing a heavy trailer up a long, steep grade. But don't exceed the max temps for motor oil, ATF, gear lube, exhaust gas temp (EGT) and engine coolant. That means you gotta have good gauges for those components.
Never exceed 1,250° F. pre-turbo EGT. Never exceed 225° tranny sump temp. Never allow the engine oil temp or coolant temp to go into the red zone on the stock gauge. Never exceed the manufacturer's weight ratings of GVWR, GAWR, GCWR, tires, receiver, etc. Never drive like an idiot teenager showing off on Saturday night. Pedal to the metal is fine as long as your fluid temps and EGT stays within the green zone.
I bought a new Ford diesel pickup, and followed those rules fairly closely. I exceeded the GVWR on a few trips, but not by more than a few hundred pounds. 12 years later with about 200,000 miles on it, I sold it for one third of what I paid for it new ($10k vs. $30k). It was still as good as new. Last I heard, several years later, it was still going strong.
Change the motor oil as required by UOA (used oil analysis).
Change the ATF at least as often as required by the Owner's Guide. And use the correct grade/weight/spec of lubes per the Owner's Guide.