My son was prescribed a PPI for his ulcers as well. The first script we got wasn't strong enough so the GI doubled his dose and it did the trick. He had to be on iron supplements and Prednisone at the time, which upset the stomach so I think that was why we needed the higher dose.
He took them an hour before dinner, it took about 2 weeks before he really started feeling better. We told him just to avoid foods that upset his stomach, which weren't many.
He was able to go off the PPI about 5 months later. GI wanted him off the Prednisone and Iron before we could get off of it. He hasn't needed them since and seems to be fully healed.
I think the liquid diet would definitely help, it wasn't necessary in our case.