I completely understand your frustration. In my case, there's no way to know for sure which of the multiple causes I have was the final straw, and now I've been told abdominal surgery could kill me (because of one of my rare conditions). I don't have the vomiting, just the weight loss because of pain and food sitting so long that I just couldn't eat any more. I was put on TPN and that's how I gained the weight back. But we don't want to do anything long term if we don't absolutely have to. Still, the frustrations are there because this will be happening forever with me.
The best thing I can say is keep seeing more doctors. When you find one that really understands GP you'll have better luck with finding answers. Just be prepared and understand there might not be an answer for you. There are no cures for GP and all of the treatments have difficult consequences. We each have to find a treatment that works for us.
On the food angle, since you're not trying to lose weight (some people are overweight and trying to lose while dealing with GP) focus on things that are simple carbs. Always keep them nearby. You can do things like jelly beans, gummy fruit snacks, hard candies, etc. When you suck on them the carbs will be absorbed through your mouth. It will help power your brain and will help give you energy for your digestive tract to work (a little better). Also try making smoothies out of simple ingredients like nonfat yogurt, applesauce, and carnation instant breakfast. Fat and fiber are the hardest to digest macronutrients so keep those low and focus on more carbs with some lean protein. this doesn't mean only eat carbs but focus on them. When I was at my worst some days the only thing I did was suck on gummy fruit snacks. It got me through the day and the next day I added a few bites of something else.
As for my doctor, I've been going to Froedert and Medical College of WI which is in Milwaukee. They have several GI doctors on staff, so you can find their website and call to see who can get you in soonest. Make sure to mention that you were diagnosed with GP but want a 2nd opinion and better treatment options. As the doctor said to me, there's a difference between gastroparesis and just slow emptying, so they will probably redo the tests and some others you haven't had done before. (He's requesting my records to see what else he wants to test me for.) See if you can send your records to whatever doctor you're assigned to before the appointment, or if you should bring them with. I'm certain they will want to see them. You'll also have to fill out paperwork they will send to you.
If you haven't read what I've posted on our team about the GP diet and how to figure out what your body will handle, here's the short version: start out with the simplest foods you can imagine like liquids or very soft foods. If you can get that down and keep it down, then slowly add no more than 1 new food every 2-3 days. It takes 24-48 hours for food to go through a 'normal' GI tract and can take even 72 hours for those of us with a slow GI tract. So if in those few days you have a reaction (pain, bloating, vomiting, etc) you'll know what food is causing it. Over time you'll build up a list of what foods your body likes and doesn't. This actually works for anyone who has any digestive problem, as another of my sparkfriends thought bananas were a problem until she went on an elimination diet and found out she's reacting to the gluten she'd had hours or a day earlier. Also, don't drink liquids while eating solids. Drink water before a meal or after a meal not during (unless you need a sip to help swallow). Avoid eating and drinking cold foods whenever possible. Just like when you put ice on a bump to slow the blood flow (which causes a bruise) and dull the pain, putting ice water into your stomach will constrict blood flow and slow the nerve signals, which can make the GP worse. Go for lukewarm water or cool if you must.
In addition to acupucture (I've never tried it so I can't give an opinion but I've heard good things) you can try getting massages. Not only will they help you relax but it will help get the junk that builds up in your mucles and joints from not getting proper nutrition. Also try different positions such as walking around after eating or really focusing on standing up straight so your stomach isn't crunched or crimped. In rare cases (like me) laying down might help, but for most people it will make it worse.