Mine has a fresh SM flywheel/clutch & front bearing carrier. Haven't checked, but assume it doesn't have the rear damper.
The chatter in mine is only at very low rpm. Seems like it could be a resonant vibration/chatter in relation to each diesel combustion pulse & limited load thru the driveline. You don't hear/feel it except idle/low rpm no-load in 1st, or low rpm starts in 2nd in summertime temps. No unusual noises above say ~ 1200 rpm or other normal driving conditions.
Don't know that this additional damper the GM document suggests would eliminate the chatter. Seems possible/likely it might - for GM to recommend the part w/ going back to SM, but guess I won't know unless I add the damper. Believe SlimShady did add this damper; don't know if he'd driven the truck w/ SM & no damper first, so he'd have experienced the comparison? Guess if I decided to drop the trans to consider adding the damper, I'd prolly also go thru the tranny looking for any obvious signs of dmg or excessive endplay/tolerances.
I've only gone thru a couple automotive manual trans. The ag/tractor trans I've been into seem to tend towards opposite ends of the spectrum: either in good shape/wear patterns, maybe just reset endplay tolerances w/ shims or new bearings - OR - things went very wrong, something broke (seems to always either fall into the works, or clearance is tight enough on the bottom that a gear somehow re-grabbed a broken bit & fed it thru the works more than once), & some expensive/initially tight clearance parts are now junk.
