An output speed sensor failure (easy replacement on front exterior of transmission) will cause issues with speedometer, odometer, and cruise control, all at the same time. The transmission will also go into limp mode and not shift beyond second gear. What rpm are you getting at highway speeds. Should be around 2000 to 2200 rpm. Anything considerably higher would indicate a lower gear (second) is being used i.e. limp mode.
Otherwise try resetting as already mentioned. Disconnecting the negative battery cable for 10 minutes can sometimes get rid of problems (basically a computer reboot).
A weak battery can cause weird things to happen as well. Any idea of the age of the battery?
2007 GC SXT - Magnesium - S&G - 3.8L - 145,500 kms
2002 GC Sport - Stone White - 3.3L - 328,350 kms
2003 Jeep TJ Sport - 4.0L - 258,980 kms