I'm in the same boat as you. I just misplaced one of my fobs on my '06. I had the dealer install a factory unit in '08 and got 2 remotes with it. I just bought one from eBay and looked for instructions as well. I spoke to a friend who happens to be a service manager at our local Chevy dealer and he said something about using the "lock" and "unlock" buttons on the fob at the same time, alternating between the 2 buttons. I'm going to look further into that and see. I might get some time this week to try it, but have had a procrastination streak lately
. I'll post any results I get from trying this method. Hopefully the method I get to work on my '06 will also work on an '08 model. I know you hav to re-synch all the remotes at the same time for them to work.