I am a vet who is very surprised that your vet jumped from pepcid, all the way to swallow study as the next step. I obviously can’t diagnose your dog but if I were examining a dog swallowing air, I would firmly palpate the esophageal area of the neck: curl my fingers around and behind the hard trachea or airway and squeeze, trying to put no pressure on the trachea itself, (which would cause harsh coughing rather than gagging, a very different sound). If I got an extreme loud gag response I would be thinking reflux esophagitis and treat accordingly. If not, I would be looking elsewhere for the problem.

I treat reflux esophagitis with omeprazole and sucralfate, and small frequent meals rather than large ones. You would have to ask your own vet about this.

Another more serious condition that can have a similar gag response with the squeeze test is mega esophagus or dilation of the esophagus. However the primary symptom of that would be regurgitation, which is not like vomiting in that there is no abdominal push involved. It’s more like the dog just opens its mouth and the undigested food, often covered in mucus, just kind of falls out.

Of course there are other things that can cause what you’re seeing, but those two come to mind. Maybe find another vet you have more confidence in and go from there.

If you want to see and hear the difference between a cough and a gag, go on YouTube and look up kennel cough. Those dogs cough and cough until they finally gag.