Vehicle stays on while key is taken out of ignition on a 08 gmc envoy
Bad iginition switch.
you just need a new ignition cylinder. They only cost about $55-$60 online, and takes about 1 hr to replace it. There's youtube videos on this for GM vehicles. It's actually pretty easy once you see how to do it.
Search GMC Envoy Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
GMC Envoy Experts