Go to GMPartsDirect.com, enter your VIN, go to the suspension section, and look for your shocks, based upon your RPO codes. You should find what you are looking for at a cost that is significantly cheaper than the local dealer.
Also, if you do any wrenching, this is a job that you can perform mostly by yourself. Lots of YouTube videos that you can view for the step-by-step replacement process.
If your truck has front struts, then I recommend that you remove the entire existing strut assemblies, take them and the new front shocks to a local auto repair shop, and have them dissemble the strut assemblies using their heavy duty spring compressor, and give you back the strut assemblies with the new shocks in it.