As for ulcers - one of my mares was scoped and found to have severe bleeding ulcerations all throughout her stomach and she had none of the typical signs except she was a hard keeper. She was shiny and gorgeous, getting straight A's on vet scores at endurance rides, but she was spooky as hell. She could bolt and spin on a dime with no provocation. It got worse and worse until I took her in.
I'd been told that ulcers causes colic, poor coat condition, diarehea, hard keeping, girthiness, cranky, hates to be groomed, pot belly, general look of unhealthy, etc. She got the runs when she was nervous, and she was a hard keeper and that was all. She was the picture of health and vitality. She was energetic, full of p&v, and her coat was gorgeous. She had a deep rich glow with dapples and everybody oohed and ahhhed over her. But she was full of ulcers and believe me, I was pretty surprised.
If you want to try a trial run, you could buy the brand name Ulcergard and give a full tube a day for a week, but even that is expensive, and 1 week might not be enough. My mare is a pretty extreme ulcer case that has to be managed daily. I have switched to using this product: Welcome to OxyHors - Oxygen products for the Equine Athelete
OxyGen Ulcer Stop. I have had great luck with that company, and the product is good also. It uses generic omeprazole but given the cost, I had to switch to something more affordable.
You could even try 1/2 dose of that daily for 7 days and see what happens.
My horse now has hind gutt ulcers, and unfortunately the only thing that helps that is to rest the colon with a soft soaked diet. Antacids acid blockers, and proton pump inhibitors are not effective against hind gutt ulcers. My mare eats a lot of soaked pellets and beet pulp, and only half the hay she used to eat. This helps the colon to be less irritated and she's doing MUCH better with this diet.
As gross as it seems, you should go out with a flashlight and a stick and pick through the loose poops and see if you can detect any tinges of blood, or even a lot of mucous is a warning sign of hind gutt ulcers. Blood wasn't showing up on my horse all the time, but ocassionally I could detect a little string of bloody mucous. You can also do a fecal blood test Succeed - Equine Fecal Blood Test™
to check for blood coming through the digestive tract. It's not very expensive and it would let you know if any blood is detected and where it's coming from. Sometimes the blood is there but not visible to the eye.