Although I have many Haynes manuals and continue to buy them, I am generally disappointed when I use them. I recently wanted to know about the PCV valve (like where it is and what it looks like. The picture in the book looks like it is from a mid 70's car, not a '99. This is quite common for Haynes. Their books go into great detail on easy things like unbolting an alternater, but are very sparse on more difficult things like transmissions, emissions, ignition, torque specs, capacities, and wiring -- exactly the things I need vehicle specific information on. Haynes manuals pale in comparison to more comprehensive manuals published by Bentley. I have a Bentley manual for my VW, I wonder if there is a similarly conprehensive manual for Chevy trucks. I will look.
P.S. If you know very little about mechanics, a Haynes book is an OK start, but you outgrow them fast and you will be frustrated trying to find simple info such as tire pressure.