2004 GMC Envoy XUV/SLT; How to change third brake light

Never mind, I decided I will take this to the dealership. Mainly do to two reasons (well three); 1) I can't seem to find the correct part, I been sent the wrong part by two different companies. 2) you can not access the third brake light by taking off the inside tailgate cover. There are three screw that need to be removed so you can remove the trim the light is in. There is a screw on each end of the trim you can access by swinging the tailgate open, and one screw just above the wiper. You will also need to remove the wiper arm. Knowing the problems that wiper arm can cause with the proper functioning of the tailgate; 3) I didn't get any response to my question. So this one is worth taking to the dealership.

To remove the third brake light on the GMC Envoy "XUV" open the tail gate and at the top far ends of the tail gate there is one screw on each end, remove the two screws, then close the tail gate and remove the windshield wiper by using a flat screw driver and prying on the wiper base, then remove the screw that's right there below the wiper base and the complete third brake light assembly will come off.

Is there any light bulbs or do I need to replace whole third light assembly

You have to replace the whole light assembly. GMC didn't make many of these vehicles so that part is difficult to find. I had to replace mine seven years ago, and it was difficult to find that assembly at that time. I can't remember the cost, but it was extremely high for jus a third brake light.