I completely agree with Dr. Coyner. Chronic Vomiting and Diarrhea are very serious symptoms and along with the weight loss we are concerned. Sounds like the basic things have been looked into. Parasites, Pancreatic problems, etc. Now it is time to medically investigate more closely.
I would suggest you see an internal medicine specialist. There is probably not one in Steamboat, but in Denver I recommend the VRCC - Veterinary Referral Clinic of Colorado at 303-874-7387. They have a team of internists and outstanding facility and expertise. Call them today as it may take some time to get in. I know it is probably a 4 hour drive for you, but they are probably the closest. CSU is also a good option. You will have to look at the map and see which facility is closer.
Good luck and let us know what they find.
I'm so sorry to hear about your dog, with the diarrhea and weight loss, I would be worried about an infiltative disease of the intestines causing decreased absorption of nutrients, such as inflammatory bowel disease, lymphagiectasia, or intestinal cancer. Pancreatic insufficiency can also cause diarrhea and weight lsos, but I assume he has already been tested for this when you say his pancreas levels are normal. Ideally the next step would be endoscopy or abdominal exploratory to evaluate his intestines more directly than an ultrasound, and get biopsies to find out why he is losing weight and determine what the correct treatment should be. Your veterinarian can refer you to an internal medicine specialist for further workup and treatment, or of course you have a great veterinary teaching hospital at CSU in Ft. Collins.
Good luck,
Kimberly Coyner, DVM DACVD