xcel
If you were actually driving on some type of surface, the speed is pretty irrelevent. But, there is a crossover point (Had to look this up on the internet) along the way. If you can picture driving away from Earth, Earth's gravity gets weaker and weaker, while the Moon's gravity gets stronger. In effect, you are driving "uphill" to a point about 207,000 miles out from Earth (that is the crossover point) from there, the Moon's gravity is dominant and you are driving downhill for the remaining ~43,000 miles, so don't ride the brakes too much at first...you're gonna need them later!
Skypig
Actually it's a 3800 HP, 16 cylinder diesel locomotive engine. Every time the oil prices spike up, all the crack-pots come out of the woodwork with the latest fuel saving additive or device. Magnets, mixers, fuel catalysts, blue marbles, you name it. So I have to take a break from real research and test their schemes. Latest guy claims savings with his additive after "only" 5 tank-fulls...which happens to work out to the 23K gallons.