4 Wheel Drive/SUVs: towing a trailer on pavement in 4 low, pound trailer, bad habit

Question
I went camping with some friends for the first time, and the road was so steep that my transmission was overheating pulling a 10,500 pound trailer with my F250. When I got there I asked my friend how he does it and he said for years he has pulled the last 15 miles of the trip in 4 low because the gearing is better. I want to know how bad is that on a truck and what would it wear on the most?

Answer
The front axle. This is a bad habit to get into. When in 4 low the front axle is turning a fraction slower than the rear so it binds up the transfer case resulting in gear lash casing broken parts later. Also the front axle will almost literally explode due to the lash you are creating