The lower payloads of the of 150/1500 is weak point of trying to tow a tongue heavy trailer (almost all toy haulers). If size is intimidating, look for an extended cab short bed - My F250 was just over 19' long and under 7' tall allowing it to fit most parking garages.
You can get a truck with a gasoline engine to save some money and it will pull great on the flats. Unless you plan to spend most of your time towing at elevation, you will not need the diesel. I will warn you that if you buy a diesel, you may never go back to gasser except for financial reasons. The pulling power of these modern day diesels will but a smile on your face that will just get bigger as the grade gets steeper and longer.