we have a 1999 Freightliner FL-60 four door, when I was looking I talked to my buddy that drives tow truck and the company had International and Freightliner he has a lot of time in both trucks, and he said Freightliner hands down for power, handling, the ride, well we listened and found ours on ebay for $30k, I towed my 42 foot fifth wheel toy hauler with my 1990 dodge diesel SRW and with my Freightliner, that triple air ride system of the Freightliner makes a 500 mile trip seem a walk in the park, now as far as the CAT motor, we got lucky and ours had been rebuilt by CAT and had 2K miles on it when we got it, our trailer is 16,000 and the truck with full tanks and tools is 13,000 so without a doubt we are NOT the first people to the top of the hill, but we are the most comfortable going up and coming down, have you thought about stepping up your game and going with a full semi built for towing RV's ? heres a picture of our truck and trailer >>>
http://www.pinterest.com/pin/551339179353517264/