why my 2004 m special jumps out of gear when the car slows down

THIS SOUNDS LIKE A MECHANICAL PROBLEM NOT A ELETRICAL/ COMPUTER PROBLEM, IS HARD TO KNOW WITHOUT SEEING VEHICLE, CHECK ENGINE LIGHT ON? ANY CODES?

There are many electronic controls that directly and/or indirectly can affect the transmission operation. You have some type of electronic problem and/or you may have an internal transmission problem. The first step is to diagnose the vehicles electronic transmission control unit and electronic solenoid operations. This will in turn determine the source of the problem. This test runs $ 89.95.