http://www.electricmotors.machinedes.../bdeee1_1.aspx
Mainly look at it in terms of acceleration vs. top-speed. You will have a lower starting torque requirement with a higher gear ratio but lower top-speed. So, that's quicker. So, in a truck - maybe gearing of 20 pinion, 80 spur gear. For top speed, a lower gear ratio would allow for slower acceleration but higher top speed (24/80). The motor spins fewer times per mph, for example. Since constant speed is fighting wind resistance and other forces - you are always accelerating to maintain a constant speed. Power is lost due to friction and a little but due to sound and even light (sparks in a brushed motor).
I think that the paper in the URL above could help give answers to what you're after. Everything would break down to simple fulcrum forces (lifting weight by a lever) - just keep the motor's wattage in mind when considering power. I think electric motors have a rated wattage which gives you a starting point for power-output.