After discovering the lack of ulcers, I've changed my tactics with Thomas a bit. Basically, I'm cutting him very little slack. He's been pretty good. A couple of minor shutdowns daily and then much improved work towards the end of a 45 minute session. Today I was riding with the big arena doors open, and no bulky parka! Hurray! I cooled Tom out with a brief hack down the road. He was fine until a pick up truck came up behind us and he kind of blew. But that's what he does and that's why I rarely go out for hacks alone.
My latest quandry is that I've been reading that people with EPSM horses have had trouble with their horses reacting poorly to vaccinations. Tom has never shown any adverse signs, but it does make me wonder. I'll be running that by my vet when she comes out next week to do his shots. I'll also have her check his insulin and Vitamin E/ Selenium levels, just to keep tabs on them.