Well I have a SCREW FX4 with 3.73's and I hand calculated over 20 on my way to Los Angeles from Napa. And I used to religiously hand check my mileage and it was never off be more than 1 mpg, in fact it was usually within .5. And it usually hand calculated to slightly lower than the dash, but sometimes the dash was pessimistic.Mine is 5 to 7 percent off. Those of you that rely on the dash computer versus hand calculations are in denial. Those of you that drive a 4x4 rely on the dash computer and claim getting 20 mpg are full of you know what. Your mileage may vary. Bob