Photos 1 & 2: Are the roots packed with some sort of peaty potting soil?
This Spring, take it out of the current pot. You're attempting to fix the roots. Small pots will keep you from doing this. Get a restaurant bus tub, 7 or 9 inches deep.
Here is the potting criteria:
1) The tub needs to be deep enough that when filled with water, the water level is at least an inch above that peaty black soil I see in the first photo.
2) The soil isn't much deeper that its current potting level. Maybe an inch deeper if the tub is deep enough to accommodate number 1, above.
3) The top of the soil isn't any higher than it's current level with respect to the tree.
4) The soil should have 50% inorganic material 1/8" to 1/4" in size, and 50% anything organic, pine bark mulch, garden soil, potting soil..., so long as it doesn't just turn the water into soup.
Leave the tree submerged in water from March to October and draining water for the winter. Oh, wait, you're in New Mexico; high desert. You'll need to adjust the schedule so that you're drowning the tree from buds swelling to before the first freeze. Once you've punched holes in the tub to drain the tree, you'll need to nest the tubs to keep it drowned from Spring through Fall.
Ok, so why do all this? The roots look like crap. You didn't grow the tree, so don't be insulted. Whoever grew this tree wanted it to look like it was left in a 4-inch pot for much longer than was aesthetically pleasing to do so. Or they forgot it. I don't care which.
Leaving this in water will cause the roots, including those pillars we see now, to swell big and fat. They will grow splits in that gray bark and erupt in yellows and oranges. You may only need to do this for one growing season. If the tree looks good by the next spring, you're on your way to doing something else. Otherwise, keep drowning/draining for another year.
These techniques work here in NOLA. BCs are not native to the NM high desert, so your mileage may vary.