I know for a fact that my Jeep gets better gas mileage when revved out to 3,000rpms (our peak torque in the 4.0) than driving it at 2000 in every gear. The 4.0 is a torquey engine sure, but it just doesnt have the power to move the Jeep around in the wind. Low speeds its great, but its not exactly the most efficent motor for moving our refrigerators down the road. Rev that bad boy out a little to help out. Lugging the engine is not a good idea in ANY vehicle. 1/8 throttle at 3,000 rpms is going to burn much less gas than 1/2 throttle at 2,000. In a Jeep, throttle position is much more important than Rpms. Now in a Camaro, its the opposite. Reason being is that the motor has more than enough azz to move the vehicle forward, so the less gas AND RPMs the better (less fuel consumption period). This works, because the motor will pull the vehicle through a flat road at 1/8 throttle 1800 rpms, as well as up a hill at 1/8 throttle 1800 rpms.
Short and sweet, in your Jeep, rev is out a little with less throttle opening. In an over powered vehicle, drive with an egg under the throttle and shift early.