Other Fuel System Tank Filling/charging problems of the 2004 Chevrolet Impala

Hello, I just purchased this vehicle from a used car dealer and drove it to work two days later. I work an hour away and take the turnpike. . . . I noticed while I was driving that the speedometer was near 90, and when I pulled into my jobs parking lot I was near 40 mph. . . The parking lot's speed limit is 10 miles per hour with speedbumps so I knew somethinig was wrong. When I got off of work my gas tank read past the full mark. . . . I have been filling the tank every other day to prevent being stranded. I immediately called the dealer and he took a look at it. I purchased the car on 01/17/15 and today's date is 02/01/15 and I am still waiting to get the problem resolved. I've researched online and seen a lot chevy Impalas have this problem. Most notably 2001-2005 I would be eternally grateful if the matter can be resolved. Thanks, khadijah s ligon p. S. There weren't specific options for the problems. They are:the gas gauge, speedometer, the whole panel. . . . I found out this is called a cluster? or cluster panel?.