Not used Gastrogold, however my TB has been diagnosed with some grade 1/2 ulcers (fairly low level) and they were blasted with about 7 days of Gastrogard and now he has a supplement called UGard Plus from Equine America in his feed twice a day - this was at the recommendation of the vet. Month later signs are good - he's filling out nicely and seems much happier in himself.
My vet also recommends Equine America's U-Gard Plus & uses it on her own horse. It's made a big difference to mine, I did try the Gastrogold alongside Biotal Gold (they sent me three months supply of both to try when I asked about it) but it didn't work as well for him.