WALK! 186000 miles? It better be a Diesel! If you are going to get something with that many miles on it, Check Ebay Motors and get a Diesel. The engine will last longer, it will pull the next 2 RVs if you upgrade and you'll get decent mileage.
That switch is only for trailer mode which leaves the transmission in lower gear longer for hauling uphill. Crew Cab pickup especially if your family is growing. How many people are you taking? If that is reason for the Yukon XL, Look for a Ford Excursion, they came in Diesel and will haul what ever you want.
