when you try to accelarate it wont go further than 5 mph.
There is a light that comes on and states "LOOSING POWER"? on 2002 Saturn Vue
The car/engine must be going into limp mode to prevent itself from damage. In all likelyhood a scan tool is going to be needed to retrieve trouble codes stored in the computer of your car and a professional grade scan tool will also be able to monitor live sensor data to whats going on.