Profile For David G.

I don't know this for sure either, but if I understand it correctly, the engine brake is exactly that, a brake. And in slick conditions, you don't want to ride the brake, as that can cause a slip or spin out. By down shifting, you lower the rpm's, thus slowing your speed, and the torque, which can also play a part.

Just my 2 cents worth.

The reason you should not use the jake in slick conditions is because it multiplies engine brake force. Take your foot off throttle at cruise speed and the truck slows a little, use the jake and it becomes more. Because the effects are instant on deceleration, if you take your foot off throttle, the response is instant and abrupt. Using lower gears is a conscience decision, and not reactive as the jakes. They also say it because downshifting with the jake on when slick is most often catastrophic. Its also easy to forget that its on. The cruise can not be set on my truck (2015 Cascadia) if the jake is on for that very reason.