Is this dog actively vomiting (retching, dry heaves) or is it regurgitation?  Regurgitation is a more passive process so the dog can just lower their head and food comes up. If this is the case has your vet checked for megaesophagus?  This can usually be picked up on a chest xray as opposed to hiatal hernias, or IBD which often needs endoscopy to diagnose.

This is not something that is normal after an amputation, even for deep chested dogs.  Did anyone say if he regurgitated post-op?  If so he may have an irritated espophagus or stricture and that can sometimes be seen with a barium dye study.

Is he completely normal if he takes the Cerenia?  If so then he must have some amount of nausea.  It is okay to give this daily with the sucralfate and pepcid although if I need a drug like this long-term I sometimes have better luck with Reglan (the generic is metoclopramide).

Feeding him in an elevated position or trying different food consistencies (canned vs raw vs soaked kibble) can help.  Some dogs can also respond to a novel protein such as venison or duck or even a hydrolyzed diet like Royal Canin HP.

Pam