Manual transmission is definitely the way to go if you're going to develop ecodriving/hypermiling techniques. The EPA ratings comparing an auto vs. manual transmission for the same car may not be that far apart, but in the hands of a determined hypermiler, they'll be
miles apart.
http://auto.howstuffworks.com/torque-converter4.htm
A lock up torque converter makes a direct connection between the engine & transmission, typically in the highest gear, once engine & transmission speeds are close. It improves efficiency by eliminating slip between the 2 sides of the fluid coupling.