The first thing that would greatly improve SRP would be a rework for the Rocky Mountain Elk. EW has shown that they can make a great elk model in the case of the Manitoban Elk on Askiy Ridge, and the RME deserves to look just as good or better. In the thread there are links to multiple posts that explain how this species should be reworked. The Plains Bison, Mountain Lion and Merriam Turkey could also use some major improvements to their models and textures.
In addition, I also think that the Pronghorn drink time should be moved to daylight hours since this species is not nocturnal in real life. In my opinion, Pronghorn drink time should be moved to 12:00 - 16:00, the same time as Bighorn Sheep, because the water sources in the areas where the Pronghorns live are totally barren during that time of day currently. They should also be moved back to Class 4 because that just makes far more sense for realism.
I also think that Mountain Goats should have their population redistributed across more of the map. They should only be found in the high mountains in the central and northern parts of SRP (I have a map below that shows where I think their home range should be). Everywhere else is either too low in elevation or too forested to be realistic habitat for them.
This map would also benefit from backfilling. Backfilling waterfowl species would help to bring more life to the many lakes and ponds. Backfilling more small game would also help to diversify the map's animal roster. Here are some species that would be great backfill options:
Dusky Grouse
Coyote
Cinnamon Teal
Northern Pintail
Gadwall
Red Fox
White-Tailed Jackrabbit
Bobcat (if they get changed so that they no longer spook larger animals)
Finally, I think SRP would greatly benefit from some brand new species. The American Badger, Yellow-Bellied Marmot, Blue Winged Teal, and White-Tailed Ptarmigan would all be great additions, in my opinion.