bandit86 -
Remember that the on-board gauge is typically biased in favor of the car. What jamesqf said is also very important. I have one section of the 210 West where I can get over 70 MPG on my SG, but I know it's because of a long slow decline.
The lesson learned is that if you had asked our opinion before buying the car, we would have been able to warn you. Here is a quick search of the Ecomodder Garage of "Make = Jeep", "Model = Grand Cherokee" :
EcoModder Fleet list - EcoModder.com
Of that list, I think this is the best of the bunch because it has great MPG + a lot of fuel log entries :
Kmachine : 20.38 MPG
Details: Jeep - 2003 Jeep Grand Cherokee Fuel Economy - EcoModder.com
CarloSW2