I have joined 2 groups for the 99-06 Silverado's, but so far, there seems to be no traffic on either site. Where can I go for info on these trucks. I just bought one, and need a little help in a couple of areas.
If you are still looking for info there are a number of different forums.
For relatively stock stuff and info on maintaining stock, silveradosierra.com and gm-trucks.com are good stops
For any significant modding you'll get laughed at there, so performancetrucks.net and gmfullsize.com are great and responsive to questions that get you mocked elsewhere. pirate4x4.com is good too.
If you are talking any kind of diesel, then duramaxforum.com and thedieselpageforums.com are good
There are a slew of other forums, but these are the big ones I primarily use and they have great internal search function capabilities as well.
I have a ridiculous amount of knowledge on this era truck as well (own two and maintain a fleet of others) and have done a lot of work and research on it all. Happy to help if I can.