How did the 08 rear axle rating go up by 400# yet the differential and axle shaft remain the same as the previous models? The only change was on the axle houseing and that was in regards to the suspension system.
I thought the axle got a bit larger (but only from what I read; I have no direct knowledge). It did sound like they fixed a few weak links like the spring shackles. Depending on what was the previous limiting factor, you could get a higher GAWR from just bigger tires, or even higher tire pressure recommendations. Tires that aren't running at the max 44 psi get derated quite a bit, in addition to the 10% margin taken out when P-type tires are used on trucks/suvs.