Hey lourash - I don't think I'll be much help about reflux - sorry! I'd say trust the endoscopy, though; color pictures have got to be better than just an x-ray.
The big test for gastroparesis is a gastric emptying study. I think hospitals might do it in a couple different ways, but mine gave me an egg salad sandwich made with a radioactive egg - it shows up on a scan (they check several times over one or two hours, typically) and they can set a rate to how quickly the stomach empties. If it's too slow, then that's gastroparesis. It makes you feel plenty sick - after eating, or just in general!
Let us know how it goes! I hope your husband can get in for an emptying study - my doctor at the barium swallow pretty much handed me a gp diagnosis right there. I really hope something works out!