It would be a long hike if it was even allowed. It was the newest terminal. Soon to be the second newest. I see they had an open house at new terminal 3 on Saturday. Seems it will open on June 27th.
We used it all the time (D) when National airlines was in business.
It IS confusing. Reason why I thought you could walk it (if you wanted to) was the layout. McCarran always puts up signs to make you think you have to take the Tram, even when its easily walkable, especially if you have time.
The D concourse in the main terminal isn't new, although some additional gates were added a couple of years ago. I've been flying in and out of there for many years. And I've always had to take the tram -- I wouldn't even know how to get there on foot, lol.