It sure does sound like gallbladder based on your symptoms. The ultrasound would have detected gallstones, so that's not it. What was your ejection fraction on the Hida Scan? Sometimes your gallbladder can get mildly infected to where symptoms like yours present, but it's not bad enough to indicate surgery.
I had the same problem. After a week of inpatient tests, the GI doc had to discharge me. Well, stubborn cuss that I am I demanded to speak to a surgeon first. I'd had several laparascopic surgeries for endometriosis and wanted a surgeon to at least peek inside to see what was happening. Even with a "normal" ejection fraction on the Hida scan, my gallbladder was so infected it was ready to rupture. Because of the infection, I also developed adhesions (scar tissue) on the small intestines that caused obstruction.
You know your body. You may simply have to back off high fat meals and wait and see what happens. If the symptoms continue despite dietary changes, it's time to have a look inside. At least, that's my personal opinion. Contrary to recent political press, surgeons really don't want to cut open a patient unless it's absolutely necessary. Sometimes you just have to keep repeating your story over and over until someone pays attention.
So, they are planning to check your gall bladder?
Ask your Doctor about Sphincter of Oddie disorder,