One thing to consider is time. That 1989, is or could easily be doing the job, after 36 years of being on the road.
I agree that the newer trucks, (as you know I had one for personal use), do the job better. They have more power, better cooling systems, bigger brakes, and so on. I am impressed with the newer style intake "internal snorkel" setup.
But the truth is, that people were doing the exact same thing in their pickups 30 years ago....hauling big trailers, hauling construction equipment. Some of those gmt400 truck still do it today. I see it regularly in Charlotte. Many Gmt800s, and many newer 6.6 gmt whatever they are now.
The older trucks were victim to emission regulations and were very underpowered because of this. The legendary GM 454, was severely affected by these new restrictions on emissions, and of course, manufactured did not know how to keep the power up, and the emissions down. I think they have it dialed in now.
I agree the 2006.5 is probably the Pinnacle of the trucks, coupling near perfect drivetrains, great material selection, and proud manufacturing.
Who is to say whether these new 6.6 truck will be on the road in 30 years, and i am sorry to say, of thing continue how they are going, we will likely not be able to see.
One thing that I think is the achilles heel of these new trucks is the electrical/electronic systems. Wire sizes are to an absolute minimum, for cost and efficiency. Sure the sensor goes out here and there, or a connector breaks, but the whole harness? One of my friend has a land scaping business. not to long ago, he got stuck in some mud on a site, the rear axle was sunk. Some back and forth, someone finally helped him out. On the rear axle is a wiring harness, part of the system that tells your brake pad wear percentage. In pulling through the mud that harness got torn out. Not sure of the extent on how much had to be replaced per dealer, but it was to the tune of 2700$ to fix. All for a system that really adds no real value to a truck.
Real truck people dont need a sensor for brake pad wear.
Point is, there is a bunch of stuff we dont need on these new things.
Would you agree?