The degree of streamlining and the size of the frontal area of any given coach is given thus can t be changed. How that shape is driven determines the amount of energy required. Friction losses are like the energy lost to heat in your automatic transmission. Automatic transmissions have a torque converter that churns the fluid transferring power between the engine and the shifting mechanisms. This causes the fluid to heat up and special radiators are provided to cool it, thus loosing energy.
Most modern transmissions have lock-up torque converters that minimize the loss of energy.
Each rotating component in your rig generates friction thus looses energy through heat. Rolling resistance is composed of all the components on the coach that have to rotate in relationship with the ground. If you look at your tires, they have a flat spot where they contact the ground. There is a bulge at the bottom of the tire where it is distorted by the contact with the ground. As that tire rotates, that bulge moves as the tire sidewalls are flexed causing the tire to warm up.