No engine braking when car is at operational temps.

When going down steep grades I shift from Odrive to 3rd, rpm jumps but car does not slow, on the brakes until the bottom of hill. Occasionally this has happened on level road, car speed creeps up when foot is off the gas, shifting down to lower gears does not slow car down, on the brakes to keep within the speed limit. Have not done any trouble shooting as I do not know where to start. All reg. Maint. Is up to date, car shifts normally at all times, throttle cable system is not binding, and operates smoothly. This does not happen when the car is cold. Any help would be appreciated. Thank you.