http://www.gmfullsize.com/tech/gmc_c...light_mod.html <-- thats the article on how to clear it.

As far as tuning goes, you fill out the form online, submit it/pay for the tune, and he will ship you a new PCM. Then you ship him your PCM for the core charge. The PCM is located under the hood and yes you just pop it out and pop the new one back in and PRESTO CHANGE-O your truck is turning into an ass kicking machine.