Shera, I have a mustang too (Kiger) and struggled for several years to get her insulin lower. I think the thing that made the difference, finally, was soaking the hay. I now buy the lowest sugar hay I can find, and soak it at least half the time for Blessing. Using only low sugar hay did not get her insulin low enough.

Blessing is also PPID, so our experience may not match yours, but I think you'll find that soaking the hay makes a huge difference in your numbers and in your horse's comfort.
--
Helen Connor and Blessing (IR/PPID)
Scappoose, OR
Member since May 2017
Case History:  https://ecir.groups.io/g/CaseHistory/files/Helen%20and%20Blessing
Photo Album:  https://ecir.groups.io/g/CaseHistory/album?id=6847