Hmmm...my '11 EXT has led 3rd brake light, and led tail light / brake lights all the way around. Maybe it is an option on the premiums? Maybe you can get one at a scrap yard, or see what a dealer would sell them for new.
As far as i know no EXTs came with LED taillights. All of the ones are after market. Also the 3rd brake light on the EXT and Avalanches are non LED
Yep....you are right chakde! For some reason I thought the tail light/brake light assembly on mine was led as well as the third brake light assembly. Only my third brake light assembly is led. I believe the '11 EXT's (not sure about earlier models) had two different third brake light assemblies, depending on the trim package.....Base, Luxury, Premium, etc.
I think there was a thread one time, that discussed the work involved with changing from a normal third brake light to the longer led third brake light. You also have to change the whole plastic "cowling" that goes across the body and connects to the two "wings". Just guessing, tho, as I cannot find that particular thread just now. Someone with more experience can chime in and help me out here