Umm... if you want to go lower than 40ish turns, you're looking to fry some FETs. Here are the basics:

Less turns=higher rpm=higher current draw
More turns=higher torque=less current draw

Also, with the 20 turns one way and 20 the other, the magnetic fields of different directions will cancel, it will not work.

For the truck, You're going to need some more torque than with the cars, especially if they have 4wd. If you are looking for more speed, I would splice in two cells and run 6 on a stock motor.