RandyW
If I needed a dually and was nearby I buy that truck at your loss (it does have a wacky clutch) and grin all the way home and fix whatever clutch problem it has.
OK smart head comment over.
Pretty sure 2018 was the LAST year for the G56 handshaker, its a keeper. That trans needs to come out and see what's going on. And pics of the clutch in particular the springs in the Self Adjusting feature. sag2 posted a clip from the FSM of it in post 22 and that's where I'd focus. As far as a new system how it feels depends a lot on what system is chosen. You can go to a non aggressive non SAC system and the pedal feel will be like an NV5600. You can install a SAC system and have a light pedal feel and enjoy the clutch. Now this is about as close to an ad as I think I've ever come but the company I USED to work for built their own series of SAC's and for the G56 they packed in more clamp load and beefed its adjustment system. I installed one for a friend in his 6.7L dually 2008? and he's ran that truck respectfully hard towing a 34' Airstream for YEARS and no issues.
Until the trans comes off, or in the unlikely event that the hydro's are doing something completely wacky well we just don't have the hard evidence.
Gary