I have an 07 Silverado(new body).  Has anyone done big and littles (265 fronts and 285 rears)?  I was told that there could be a problem with the abs system.  

I just posted the same question. I had 275/45/20 fronts and 275/55/20 rears on my 99 Silverado last year and did notice a slight issue with the ABS light when I went into reverse first thing. I would shut the truck off and restart with no ABS issues. I figured the tires were close enough in size that it might not be detected (30" tall front and 32" tall rear).

This year I want to go with 20's on the front and 22's on the rear. I want the side walls on the tires to be the same height but have the hot rod stance of bigs and littles.

I know that the Chevrolet dealership that did a recall repair to the truck did not like the different sizes. That is something to consider with a remaining warranty.  

Yeah, I love the look and am not ready to completely give it up.  I've found the right tires and wheels, but wanted to make sure that the brakes would not become unsafe in some way.  Does anyone know if the new Silverado abs system is radically different from the 99-06.