We went from 2003 GM Xcab, SB, 6.0L 3:73 four-speed w/BFG 265 tires, to a 2015 GM, Xcab, SB, 6.0L 4:11, six-speed - BFG 285 tires. The difference is quite a bit in both handling and operating on highway and in the back country. I also believe the suspension has a bit more beef ... and a bit better MPG as well.
We put 214,000 miles on the 2003, and it was not nearly worn out - but we cross-country travel a lot, and were more concerned with the little things wearing out (wires, gauges, electronic glitches, etc) the small easy to repair things that stop you dead when you're way off the highway ... so we traded in.
We haul a 3500 lb Truck Camper - so, a bit different that a TT. But the comparison with same camper on the newer truck, similar engine etc - performance was improved definitely enough to notice driving it, regardless of "any numbers one might dig up" -- Of course, the numbers matter for comparison between vehicles, but I evaluate my trucks under work conditions on the road. We'd upgrade again under the same conditions. That 6.0L engine is a true workhorse.