Xentx in Trucks

We have 4 trucks that have been using the Xentx oil treatment for almost a year now. We are averaging about 1 mile more per gallon of diesel fuel. With fuel prices like they are we are saving a lot of money. We have kept the recommended oil change schedule although the sales guy says we could do more miles between oil changes but I'm not ready to take that leap yet. It appears we have no engine problems because of the additive and our engines are running about 50 degrees cooler which I expect may increase the life of our engines.

John