I recommend Dr. David Fazzino, Cold Springs Animal Hospital in Anna, TX.
I used to board in Celina and long time ago was my vet. When my first horse became IR & C's he did the dex suppression test. I educated him as i learned more from this group. Later a friend, who also uses him, told me he had switched to the ACTH. I gave him lots of literature way back then and he came around even back then to doing whatever test I asked but now does the preferred one and understands more of the protocol. He is really nice and tell him I said hi.
sorry can't remember my year joined
but promoting this group ever since!