UPdate: I just returned from a 3,700 mile epic journey through New Mexico, Arizona, Utah and back to Missouri. I ran one quart of Marvel Mystery oil in my gas using the appropriate amount at each fill-up. In one tankfull I got 22mpg (did the math) Aside from that tankful I averaged 19.5-20.0 Click image for larger version.  Name: DSCN9137.jpg  Views: 121  Size: 94.5 KB  ID: 1346mpg which is normal for my Commander on the highway.
I attemped to add a photo of me in my Commander at Monument Valley but the uploader does not work for[ATTACH=CONFIG]1346[ me. Now the attachment appeared. I wll not know if it worked until I hit send.
HT