[piecesparts]

It is all in the gearing and the way you use the truck. If you change to another tranny, the rear end gears may need to be changed to get what you want out of the truck in gas mileage. As stated above the 4 speed is one of the most indestructible transmissions built, but the rear end is undoubtedly costing you in gas mileage. An automatic allows you to drive and NOT have to shift, but the slippage built into the fluid clutches does take away in mileage. The manual involves the driver, but when engaged, there is a direct link from the engine to the rear end. Look at the gearing and then rethink your choice for a tranny. Maybe a 3.42 gearing would work better.