Fuel economy getting worse

[jambo101]

Took the gps unit to Bestbuys where the geek squad diagnosed defective power cord, $13 later with new power cord unit works fine.
The low mileage problem is a head scratcher as last summer i got as high as 49.9mpg while crossing the prairies. wonder if the scanguage unit is defective or has had a parameter adjustment.but on the first leg of the trip it acted normal and i watched the gauge climb slowly for 15 hours, then on the second 15 hours its like it was going slowly backwards