cerbersuiam,
Well put.
But I think you can go back as far as the OPEC oil embargo for a starting or transition era for going away from cast iron and 85W140 to the alloy cases (NV5600 is the last cast iron case gearbox I think in a P/U) and anything but 85W140 for gearboxes. Fuel economy IMHO was a big trigger for the increase in complexity in this area of the driveline. Less weight throughout the vehicle, increased power output etc. and in our powerful Dodge Ram's we want gobs of TQ and HP but a quiet comfortable fully featured cab enviroment.
Clutch disc torsion dampers in the 70's used to be a classic 5 spring or maybe a 5 spring outer with 5 inner springs and not much else. I was looking at a disc from the mid 00's and it had about 20 springs in it, these often have idle stage or predamper sections to further reduce noise at idle, want to test it, next time at the drive thru, roll your window down, trans in N and push the pedal down and up several times, hear the transmission? It also changes with trans temp.
The device used to manage the creation of noise in the transmission is called a Torsion Damper, explaining how it works or what it does can hinge on the listeners experience or background. They are usually made with a series of springs, usually being activated in progressive stages, you don't need to hit the 600 lb/ft stage right off of idle and they have some sort of internal friction element applied to the slight rotation of the splined hub. Think of the damper springs as carrying the load and the friction elements as the shock absorbers, not carrying the load but at some ranges slowing the rate of change in hub rotation. As I discuss it with Tech Callers, I often re-name it to a filter rather than damper. Most everyone can understand that we want a filter to remove something un-wanted from what we do want, be it oil, air or even electricity. The spikes from firing impulses and compression cycles that any engine creates are delivered to the F/W then clutch, and then transmission, with these rapid changes in RPM you get the chance to excite the gears into making an undesirable noise. But the role of the damper is not to stop it from being created at the source (the engines output "signature") but to try to filter it from the output and make everyone happy. Next time you are at a county fair with an old engine display, look at those single cylinder thumper engines, notice them generally moving in place and a massive F/W? Try directly connecting that to a gearbox! Those of you that are A/T specialists, don't torque convertors have a damper built into the lockup piston?
In my time working with clutches, getting the pressure plate correct, not a huge challenge for the OE guys, but a big challenge to the engineers that put together the torsion damper section of the disc. My first exposure to this was back in the mid 80's but today with the advanced data acquisition electronics and others, it has come a long way from lets try this combination of springs next.
Attention: TDR Forum Junkies 
. I have made the same trip for 18 years and in this truck since it was new. I have never had a problem hauling AZZ up any of the passes with pretty much the same load until the last couple years and this one in particular because I didn't like the sound of the transmission in 6th. no problems in 5th at the same RPM's. sounds to me like it is coming from the bell housing area that is why I initially thought it was the clutch. I have inspected the exhaust to see if maybe the torque under load was causing some sort problem there but have found nothing wrong there.
but the transmission issue needs to be addressed ASAP!
