Binger: given that it's a 3-speed, I think you'll
definitely find it more efficient at 45 vs. 55. As dcb says, you just have to decide how long you want to spend out there.
Can you work a soldering iron? You could find out for sure by making yourself a MPGuino.
KJSatz: I
rarely drive auto transmissions, so I can't tell you whether P&G with the engine on in the glide works. Maybe someone else with experience will chime in. Or you could take your own advice and try it
. You'd want to have fuel economy instrumentation though.