Re: 2007 Commander transmission down shifting
No check engine light on? If the TCM finds a fault, it should light up the check engine light. Are you sure its in 4th gear and not in 3rd (limp home mode)? After you switch ignition off and start again, it will go into 5th gear?
But even if no check engine light is on, i would first take it to some place where they can put a scanner on it to see if the TCM has set any code. If nothing comes out of that, i would start by changing the TPS.