Burning Oil

I have a 99 Dodge Ram 1500 with 31K miles and a small V8 maybe a 318 engine. As you can tell I do not use the truck very often. I have noticed that the truck has been using more oil between changes than usual. One time in the fall I took a long trip of 600 miles, and after coming home I checked the oil and noticed I was down 3 quarts of oil. I do not see any leakage on the ground or on the engine so I must assume that I am burning it. What would make a truck with only 31K miles start burning oil?

Just heard from my mechanic all compression readings are good and no visible signs of oil leakage.