I guess I am an old guy and do not get it. When I drove my first M1008 it sounded like it was buzzing at 50 mph. I could run it around 45 to 48 and get close to 20 mpg running down the road. It was a sad day for me when I got plowed by a Suburban.
When I finally picked up my new to me 2nd M1008, that old buzzing at 50 was back. When you are accelerating moderately, does yours shift firmly at about 15 and 25 mph? High gear under acceleration at 25 mph and we expect that gear to take us to 75? Have you tried mashing the throttle for a down shift to passing or second gear? You should find that rare to impossible over about 35 mph. Listen to it accelerate, that engine is humming at 50.
The trucks are just geared low, the engine was designed to turn slow. Unlike a screaming two stroke Detroit or a Cummins 4bt or 6bt, you cannot get away with running these against the governor for hours on end. The guys that tried call them junk because the main bearings will not stay in them. The main bearings do not stay in because the block was not up to the strain. They crack through the main bearing webbing. My buddy in the machine shop says all 6.2s have a broken block, broken crank or both. He of course does not see the ones that lived in lower rpm 1/2 ton applications.
You got a nice one, it is none of my business what the dollars are, it really does not matter what it cost. You take care of that truck and engine and it will run you for a long, long, time. You will probably get tired of it first. Pushing it beyond its design though is just asking for trouble. It is one of those vehicles you have to learn to respect for what it is. Too many guys try to make it a F250 or F350 Powerstroke or a Ram 2500 or 3500 Cummins. It is a workhorse of a different flavor. It will and can do a lot of work, just at a different pace. Glen