[Screeper]

It comes down to how hard the engine is working and where you are placing your torque curve for optimum fuel economy. Imagine your transmission got stuck in third gear and you were driving in the city. The engine would be straining constantly to get the truck moving. You would have to be hard on the gas and most of your MPG would go into the converter to generate the torque need to move the truck. Big tires have the same effect as taking away your first gear. Changing the gears allows the engine and transmission to not "see" the size of the tires. My 4:88s with 38 by 15.50 tires in gears 1 through 3 pretty much have the same rpm range as factory. Anouther way to look at it is like a bicycle. Imagine you and anouther rider are about to go up a large hill on mountain bikes (resistance) You both are equally strong and the bikes are identical with the exception that your bike is stuck in its top gear. The other rider can drop into his lower gears and pedal much more easily. When you reach the top of the hill the other rider is fresh whereas you are exhausted. Your bike would have been the best and required the least energy for long long flat rides but stop and go or up hill it required the most energy. It basically comes down to allowing your engine and transmission to work at the RPM where it is most effective. I am no expert so I hope this is somewhat understandable if not a bit wordy.

Al