Please take him to your vet and have him Bile Acid tested. I hate to have just joined this list and preach about livershunt but what you are describing are possible symptoms, such as the picky eating (im not saying all picky eaters are showing signs) but you also said bouts of hypoglycemia and drooling. High protein meals make symptoms worse. Please just have him checked, its a simple blood test that can be done at your vets office. Alot of vets dont know much about livershunts so therefor dont know all the symptoms.
http://www.vet.utk.edu/clinical/sacs/shunt/faq.shtml
The symptoms of liver shunt can start to appear at almost any age. Dogs with a liver shunt are usually very thin dogs who pick at food. They not only have a poor appetite but they can become lethargic, dizzy, and stagger. They may try to climb out of their pen, climb higher on you and cry and throw their head far back after eating, and they may go into convulsions.