I pulled a 27' 5th wheel (8500#) with F250 5.3 Houston to Durango in June 2013 in temps of >100 degrees with zero problems. The truck performed flawlessly. I drove about 55-60 the only frustration was fighting a headwind going from Amarillo to Albuquerque NM. Watch weather and leave early in day. Hills not a problem...met my expectations for a gasser. Just be sure truck and trailer is serviced. If you are going only to Durango, roads are great and you will not be in "Mountains" at all. BUT if you go further to Silverton, you WILL have problems. But from here to Durango is fine...just typical interstate hills which I slowed for, but never caused a problem. Email me if you need more info...had a great trip and can suggest camps