Seems like there's some kind of engine braking thing. I really noticed it when towing a car trailer. Going 65mph, I start going downhill and the engine needs less throttle to maintain the 65mph until my foot is completely off the pedal. I expected it to speed up but after a few seconds something kicks in and it'll stay at 65, even on steep grades where I would normally downshift in my other car. The rpms stay the same and the trans isn't downshifting. Lightly pushing the gas pedal disables it and it'll start coasting faster and faster.
My question is, what is it, how does it work and can I control it?