IMHO a 0.2 mpg difference is NOT statistically meaningful at all. Brake Specific Fuel Consumption is measured on a dyno and takes into account all factors that impact mpg - measuring it yourself via pumped gallons is virtually impossible. Air temp, humidity, tire pressure, actual speed, passenger weight[s], cargo, headwind/tailwind, headlight on/off, etc etc etc all have more than enough influence to make up a 0.2 mpg difference. Remember that the seasons have changed since you installed the hubs - this kind of test is almost meaningless unless run side by side in controlled conditions. I don't think the hubs should make that much of an mpg difference, biggest plus is that they save some wear on your CV joints.