We traded our 2003 GMC 6.0L w/3:73RE with 215,000 miles - on a 2015 GM 6.0L w/4:10 ... and the six speed is awesome with that 4:10 ...
Not because the engine was worn out, it still fired up with one crank and burned almost ZERO oil between changes. It was other components that made us trade, in part because we were beginning a six-months tour of the country, and didn't want to take chances with problems on the road.
That 6.0L gas engine is a true workhorse ... and my choice every time I'd buy a truck. We haul a 3000+ lb truck camper on it, and sometimes tow a bike trailer. Lots of miles, minimal problems over twelve years.