I use the Chevron fuel injector additive - Techron- usually after every oil change. GM sells something similar at the dealer, but from my understanding its the same exact thing as the Chevron additive, just in a different container.
I started using the additive because of my one experience on my 2000 Silverado. I was in the middle of nowwhere and the only gas station was Arco. The next day my Silverado was spurting and jumping like crazy. I remember it barely started. Brought it do the dealer who said I had used cheap gas. They poured in some of the GM additive (Chevron Techron) and it fixed everything.
Now, as a precaution, I use it just to keep her clean and running smoothly.