Convert fuel level sender resistance ranges - good Arduino project?
The Toyota sensor may be using 12V instead of 5V, which would mean you'd need to use a voltage divider to get it down to the range that the Arduino analog inputs can read.
You will need to find a digital potentiometer that can handle the voltage range that the
GM controller wants to see.  This may be 0-12V, which would be a problem since the AD5206 is only good for 5V.
However, as dandavis implies with his RC filter comment, you may be able to simulate the full 0-12V range with PWM, where the Arduino pin drives a transistor to chop up the 12V, and an RC filter smooths the result for the GM control unit.  That's probably your best approach.
Alternatively, if the GM controller is only looking for a go/no-go level, you can use the
transistor to switch in a simple voltage divider to get the right voltage from 12V.
The sensors are (presumably) just variable resistors (2-terminal) not full 3-terminal potentioneters.  They will most likely be using a series resistor to make a voltage divider, and the control unit (or gage in the Toyota) will reading the resulting voltage. You will want to either find out the value of the series resistor or measure the voltage that the gage sees.  It might already be in the 0-5V range.  The GM control unit may have the series resistor built in (or be using a current source), in which case you should measure the voltage its sensor input sees when you give it the max and min resistance.  This will be good to know when you are trying to drive it with your own circuit,