I have a GMC envoy 2008 the coolant is starting to get used up really quick on short trips & boiling. I use dexcool like required. Could the thermostat be bad seeing how I find no leak anywhere

Hello, a thermostat concern will not cause coolant to get "used up". Coolant is not a consumable item; the only way you lose it is through leakage into the engine or externally. I would start by performing a pressure test of the cooling system to expose any external coolant leaks. If there are none found, and there are no air pockets in your cooling system and your level goes down, you have to consider inside the engine for where the coolant could be leaking. It would be quite unusual but possible. Hands on testing is needed.

*Ever see* excessive white smoke (steam) from tailpipe ?