You're thinking of the "money muscle" which is on the outer edge of the butt, opposite the bone (or where the bone would've been if it was boneless).
I've been playing around with charcuterie recently and exploring the musculature of the butt (heh). While making sausages last night I was able to isolate the money muscle while leaving it attached to the butt before grinding it all up. This is a technique I think I'm taking to competition with me in a couple weeks, in theory doing it this way will allow us to present a money muscle with bark on 3/4 sides instead of just 1/4 sides.
You're right, a sliced money muscle will have the appearance of a sliced tenderloin and the succulence of the rest of the butt, except it is the most tender part of the butt. Slicing a money muscle without having it fall apart takes 1. perfect cooking
2. ability to locate and isolate the money muscle from the rest of the small muscles in that area (there's some fat seams you can follow) and
3. a sharp arse knife.
But slicing a money muscle and "sliced pork" like I think you were asking about are two different things. You can slice a money muscle out of a butt that's been taken to pulling temperatures, but if you try to take full slices they will fall apart.