Hauling heavy loads wear and tear

[flatbed94kid]

I pull alot or loads over 40k pounds and my truck I drive it very easy but it lugs because of the heavy weight. My question is and I always want light loads to save fuel. But how much wear and tear does hauling heavy loads do to my engine? I have done 47k pounds of flat steel through the mountains just crawling and sure it wears out my clutch and also like today, Atlanta, traffic was atrocious with these heavy coils, stop go, stop go, on and on. How much worse is it? What weight is to much before your doing alot of damage? I could probably do almost 50k pounds and be legal within 80,000 gross.
Other then fuel burned, brakes, how will my engine hold up?