http://papers.sae.org/820742/

"A torque converter has been developed for aftermarket use in older, heavier, large engined cars and light trucks to improve fuel economy, particularly at highway speeds. This torque converter includes an output coupled overdrive and torque split within the converter itself. This torque converter has shown gains in highway fuel economy of 9 to 21 percent. The converter changes that give the improved fuel economy result in a lower acceleration level for the vehicle"