Does your head unit load all the cd's into itself?
Or is it a separate unit like an escalade has?
If your head unit loads all the CD's in the dash, then you do not need to remove the center console to remove the radio.
Hit up metra online, or scosche. Both are vendors that sell vehicle adapters for aftermarket radios.
If you plug in your truck data, they will spit out what kit to use, then simply download the instruction manual from the kit listed and follow the step by step instructions to remove your head unit. Installation is pretty much reverse of removal.
Edit,
Download the PDF from
http://www.metraonline.com/files/products/INST-2009_web.pdf
Go to page 14 for Envoy instructions.
Go to page 13 for Trailblazer instructions.