Do torsion bars wear out?

[Marky Dissod]

I've a '04 Tahoe LT also with premium smooth ride. My codes differ as 6XN and 7XN.
I've not found a source anywhere that lists max torque for those codes.
My bars don't appear and remain elusive.

Unfortunately, they've eluded me as well.
Until you or I find a real torsion bar guru, my best guess would be -
assuming you're one of those who goes by the strictest definition of GM OE:
find an '05 or '06 Premium Smooth Ride Tahoe LT as similar as reasonably possible to yours,
use its VIN to find out which torsion bars it used, and replace yours with those.

I'd consider your situation to be a unique opportunity to loosen my definition of GM OE,
and suit things to your taste ...