Have no idea how rare that rig could be unless of course it is in primo shape and low miles but what makes it desirable to me, IMO, is the manual transmission. I think I saw one Tahoe/Yukon of that vintage and manual transmission in my shops over the years. If I was you, I would start the search for a quality transmission shop and have the one you have rebuilt, if in fact it is on the way out. What makes you say that? I would think any pickup truck of that same style would have a transmission that would swap in but you have no idea of the time left on that transmission either. Where is this Yukon at and do you ever park it outside and leave it when you are away from the house......
By the way, welcome to the forum.