When your engine and transmission and other components were new, their pistons, bearings, valves, gear, and fuel and several subsystems were clean, smooth, and working at a Holistic and prime - the new state.
That's when it took a little press of the gas pedal to zip down the road at 80 miles per hour. That's when it breaths at 25 inches of vacuum - combustion is stoiecheometic - making the most horsepower possible economically. And horsepower made passes thru to the wheels.
Over time, scum, acid pitting, and friction from the radiator engine and transmission, blocks heat flow, raises friction drag levels and makes several problems that cause running , performance, tapping, oil burn, blowby, rough shift, heat and leak problems that upset the normal performance - now worring you.