I've got 370K on my G80. I'm pretty sure the axle is all original other than brakes and seals. I have changed the diff fluid multiple times, though, and never romp on it. I think the G80 gets an undeserved bad rap from folks who abuse it.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter