Not a diesel though the truck can haul up to 9000lbs, our trailer is under 5000lbs not counting all our junk that would be in it. I haven't the slightest about a tranny cooler. I can ask my husband (he sells Chevys). If I understand you correctly so long as we are staying on the interstates we are going to have several mountain ranges to besides the Appalachians, so my concern may be moot? haha Does everyone have a favorite route. We will likely go to some unknown destination for the first night and pull into Sioux Falls for the second night (maybe longer) and then onto Custer (or there about) for the third night. It is that first leg of the trip I have no idea how to plan.