I was hoping a 100 owner with experience of this would reply but until they do -
Fuel can't burn without oxygen and the higher altitude you get the lower the oxygen air contains .
Typically, we increase the fuel flow to add a few horsepower but thats not going to work at high altitude because air rather than fuel is the crucial component .
Pump tuned to run lean , a clean or blocked EGR , high flow air filter , intercooler are all winners .
Turbo and supercharged engines should perform better because they compress air and I'm supposing a 100 series has an intercooler and turbo as standard so i'd guess your truck just needs a full service and the air fuel ratio investigated .
Petrol and diesel are different , you don't tell us which you have ?