Although "break-in" is a non-issue with most recent trucks, sometimes they do have a 500 mile break-in "Do not tow" period. Check with your dealer or owner's manual before hitting the road. I found out (after) towing about 300 miles within that 500 mile zone, that is was recommended no towing for the first 500 miles. Dealer did not tell me, I finally found that in the owners manual! I'm still waiting for the sky to fall on that one, but so far it hasn't happened. Truck is great.
Mine is a Chevy 3500 diesel duly. Towing I get 11.5 mpg / not towing I get around 15, sometimes 17 if driving strictly interstate.