Our 2004 is doing exactly the same .... so I´m figuring it´s a design anachronism. After about 25mph I feel like it´s being ´starved´ of something (air or fuel) to the extent I´ve considered taking it back to be checked out. Does yours have a weird ´grating´/´rubbing´ feeling (somewhere in the engine) after you close throttle a little .. that then goes away after accelerating again?