Wheels 18's to 20's question

This will no doubt sound like a stupid question so let the bashing begin. 2010 Sierra Z71 4WD with stock chrome 18's. Wanting to switch to stock machine finished 20's. First off, does anyone see a problem with running the 20's on a Z71 4WD. I see plenty of non-Z71's running them. Second, I noticed that the 20's are .5 inch wider than the 18's, does anyone know if I would need any spacers for this install?