This is why I avoided the painted bumper in my new '16 Sierra
My 2003 Tahoe Z71, full metal painted front and rear bumpers and my replacement, a leased 2013 Silverado 1500 Z71 with painted, metal center front bumper both had started to rust, especially from stone chips. The fiberglass/plastic corner pieces on the Silverado, PERFECT, not a chip in them.
So while my 2013 lease is almost up (March 2016), I've already taken delivery of a 2016 GMC Sierra, which I went for the SLT line to get the chrome front and rear bumper, over the painted bumpers of the Denali line, as I've learned by now, after two different GM trucks.