Even with the radio off, at idle, my FXT is so smooth, sometimes I can't even tell it is running.
Kostamojen is right; ECU reset for starters.
Courtesy of "Fast Lane" in Maine:
"The easiest way to reset the ecu is to disconnect
the cable from the negative battery terminal and
then press/hold the brake pedal for approximately
20 seconds. Reconnect the cable and you are good to go."