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http://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html That link is in the technical section, and is very informative. I couldn't find the year of your truck so that site is year specific.
I just used Epoxy based Appliance Paint on my wheels and the paint lasted for at least 5 years and still looked like new. I say it lasted about 5 years because thats when I sold the truck. I got it from Home depot. If you use regular body paint like you would with a paint code, count on repainting the wheels every 12 to 18 months to stop the rust.Heres the epoxy appliance paint