South Bend Super Street Dual Disc, 750hp, 1300 torque, 05-06 GM Duramax LBZ (8th Digit of Vin: D)

Too much torque at too low an RPM. I go back to the automatic. If you were driving down the road in automatic overdrive, with the cruise control on, and approached a hill, the system (in order to keep a constant speed) would need to accelerate. The transmission would automatically downshift in order to do so. By keeping the RPM up while accelerating, it is preserving its life. There is a misconception about fuel consumption. People believe that the lower the RPM, the better the mileage, when actually, the opposite is true. All that black smoke you get when you step on it in overdrive is unburned (and therefore wasted) fuel. Keep the RPM up by downshifting into the right gear, and your truck will run much better.

This is a very good question, because most people do just that. The trouble is, it is too hard, with all the variations in terrain, to keep a constant speed. Therefore, you end up accelerating too much in that high gear. Many trucks, with automatic transmissions, set up for towing, will include a button for "tow mode" which locks the transmission out of overdrive. The main reason for that is, the transmission would be constantly downshifting. The best answer is to say; watch your RPM, if it starts to drop too low, rather than stepping down on it in 6th, drop to 5th ...and maybe stay there.