I find that prevention is key. Smartgut by smartpak is the way to go, it’s given with their grain once a day, instead of the pastes which would be given at a show or before a stressful event. Smartgut worked wonders on my TB.
I have, with my TB mare, a year ago.. We treated the ulcers with Omeprazole, it didn't take long to see improvements! We have to give her some every fall and spring because of how sensitive she is, but different horses need different treatments!