FYI these trucks are worse than WK/XKs when it comes to spacer lifts. If you want 3.5" look at a 4" lift (BDS is my favorite this truck but there's lots of options).

For a quick and easy 2" get the 2" RC spacers and 3" rear block kit (remove the stock block). If you want more than that, either get a full 4" suspension kit OR throw on a 3" BL. Here's my Sierra with just a 3" BL. I didn't want to mess with spacers because the Denali AWD version is known to have vibration issues when you increase the CV angles.