From Riverside County to Julian, through the desert to 29 Palms, Tempe, Tucson, Calexico, San Diego and back to Riverside County, the 2007 Chevrolet Tahoe averaged 13.9 miles per gallon. At three bucks a gallon — and climbing — along with a 26-gallon tank, that’s almost $80 to go about 360 miles. In an old…