I didn't read everything, but once I saw "ulcers" I thought I would share what I found. Ulcergard and Gastroguard are the same thing!!! Gastrogauard is by prescription only, with the DOSING level for treatment (full tube), but Ulcergard (the non-presc. one) is labeled for -oops, meant PREVENTION (1/4 tube for full size horse). Buy whichever is cheaper and easier to get and use the dose your vet recommends.
If you use Sucralfate WITH GG or UG, you must stagger them because the Sucralfate needs acid to work. So you might give the Sucralfate AM & PM and the GG midday, which is what I did. And I wouldn't assume ulcers are going to heal in a few days - I think standard is one month of treatment at least. Yes, you should see some improvement in a few days, but just like taking antibiotics, you should keep treating. It also depends on where the ulcers are - I think Sucralfate helps the ones in the intestines.
GOOD LUCK- hope your boy recovers quickly and totally.