Accelerating briskly is the way to go with a automatic.You want to achieve
transmission lockup as quickly and safely as possible, then use a light load to achieve your desired speed.
Case in point.
One of my vehicles is a 2000 f-250 work truck with a 5.4 and a/t. Up to 37mph the best mpg I can get is 9-11 range. At 38 mph lockup occurs and fuel economy jumps to 19-21 mpg range. (verified by scanguage and ultraguage)
A 100% increase in fuel economy...
Automatic transmissions have certain amount of slip built into the torque converter called stall speed. That certain amount is needed to keep the engine from stalling when the transmission is put in gear and also allows the vehicle to perform as required.
Drag racers want a higher stall speed (rpm) or what is also known as a loose converter. It allows the engine to enter its sweet spot for power before transfering maximum power to the wheels.
Passenger cars have a lower stall speed or what is known as a tight converter, it allows the engine to take advantage of its lower powerband for propeling the vehicle.
(Side note)
As vehicles with automatic transmissiom age, their stall speeds can increase due to wear on the internal parts of the converter. This in turn can lead to a increased loss in fuel economy before lock up occurs. (as in my case)
So, in the end........
The sooner the transmission is in lockup and the engine is at its BSFC "sweet spot", the better...
Having a scanguage, ultraguage or MPGuino is a indispensable tool when trying to figure out the best combination for your vehicle.
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