A 14 year old vehicle with 1000 miles or 200k miles has fatigue. Springs, shocks, bushings, clutches, fluids, hoses, metal. Nothing performs better at 14yrs than new. Someone could replace/upgrade certain components to improve certain capabilities, but the sum of parts is not likely greater than when new. My point is that towing any high walled trailer near it's tow ratings for that era vehicle is likely to be pleasant, from the driver, passengers, or vehicle maintenance. I towed my TT with a a vehicle of similar vintage capability. It was acceptable 6 years ago. Had I kept that truck, I would not entertain an RV at that tow vehicle age. I would want overkill of same vintage.
Newer means lots of things. Some involve engineering improvement. Some are just less fatigue/wear.
Those points are independent of the fact that towing nearly any RV with a large family tends to put most half tons 500+ pounds over GVWR. Brand new 2017 full sized half tons with 400+hp and 8+spd transmissions have the same issues with larger families and towing an RV.