When you say dry mouth...are you thirsty? Are your lips dry as well? There are many reasons why we can have dry mouth. And high blood (hyperglycemia) sugar can only be a one of them. That was my very first symptom when I was first diagnosed with diabetes. Although, there are others, to name a few: side effect of a certain medication (like asthma diskus pumps), autonomic neuropathy, smoking, dental cavities, mouth breathing, etc. Have you seen a dental professional? Until then, try to avoid liquids and foods with high sugar content. Funny because you said grapefruit gives you relief, but for dry mouth, I was asked to limit citrus juices (like orange, grapefruit, tomato), as well as diet sodas, avoid overly salty foods and avoid rinses containing alcohol.