Tire rating is a safety issue, pure and simple...running tires overloaded could cause them to fail and unexpected or violent tire failure could dump the whole rig in the ditch.
The rear axle rating is almost always 2x the tire rating. Generally axles themselves in 2500/3500 trucks are rated at 10k+. Front axle ratings are hard to exceed unless you have the 5er hitch mounted like an air scoop.
GVWR has a longevity component to it...exceeding GVWR won't make the wheels fall off, but stuff will wear out faster then it was designed to.
GCWR has a performance component to it, meaning that you want the rig to do a respectable job on hills and on-ramps, not that you are winning races but so you are not going so slow that you pose a danger to others.
If you want some real opinions, post the numbers....
