1) If you have the factory spring clips at the base of two of your studs, discard them. They're only needed by the GM assembly line. Only factory wheels have recesses built in to accommodate them. Spacers and most aftermarket wheels do not. They make it impossible to get full flat surface friction between the wheel or spacer and the hub. Disaster will ensue.
2) Get hubcentric spacers to minimize the issue of mounting wheels slightly off-center. These are my first non hub-centric spacers. The spacer is machined properly to go over the vehicle's hub protrusion, but it's flat on the front.
This is a hubcentric spacer. Note the lip on the front that goes into the wheel's centerbore hole. These are also my current adapters, where the studs are on a 5.5" diameter bolt circle instead of the stock 5.0"
3) If you don't have hubcentric spacers, it's even more important to mount the wheels to the vehicle properly. After a lot of research, I did a bit of math, and the problem comes when you hang the wheel and tire on the studs. If you have a hubcentric lip on the spacer, it mimics the behavior better of the OEM situation, where the wheel is lifted by the beveled edge of the hub, and put within a thousandth or an inch or two of being perfectly concentric. The weight of the wheel/tire combination, that can approach 90 pounds for an oversize MT rock crawling tire and wheel, is supported by the lip and the lug nuts just compress the wheel to the spacer's flat surface.
With the cheaper flat spacers, you hang the wheel on the hub, and all of the threaded studs go to the top (12 o'clock position) of the holes in the wheel. When you put on the first lug nut, its beveled (cone-shaped) nose first tries to LIFT the wheel/tire into position. Since the threaded stud has been BENT slightly by the weight of the wheel, by the time the lug nut is tight and you start threading on another nut, the wheel is slightly lower than it should be for it to be perfectly concentric. This happens even if you do the proper sequencing on lug nut final torque. The wheel being off-center gives the equivalent vibration of an ounce or two of improper balancing weights, and you get vibration.
Two ways to avoid this:
1) Get hubcentric spacers.
2) For lower cost but more work: take the weight off the tire when you put on the lug nuts by very accurately lifting it with a floor jack into position. Make sure the lug nuts are ONLY being used to hold the wheel on, and not for the final small lifting action.