I too am experiencing the issue.
List model year. 2004
Date/Mileage of failure. Probably started a year ago. 2013.
Current mileage. 96,000
Symptoms. Grumbling around 28 and 46mph.
Corrective action. Was offered a 50% goodwill on a full trans replacement. $2850.(50%) Still considering my...
It could be a variety of factors. Have you cleaned out the EGR ports? These are known to clog and cause poor mpg.