Do not engine brake on slippery roads, that's when you need your full brake technologies (Anti-Lock Brake, Traction Control, etc.) to do the job, not your engine. I like to engine brake on dry asphalt because I want to take some of the wear off my brakes. In the E250, there's two factors when paddling down the engine to brake, one is that there's a lag, the trans doesn't have the instant response of a manual, and second, the auto trans will over ride your paddling if it thinks you will overtax the engine. So here's how I engine brake, I hit the paddle about twice and wait to hear the the engine roar or feel inertia, that I'm pulled forward against the seat belt. If I don't get that, I paddle twice more and wait until I feel and hear it, then I hit my brake. This usually is coming off a freeway to a slow or stop. I don't paddle shift all the time, I use it for special little jobs like a freeway exit or twisty turn or high speed merge. Otherwise I ride in Emode, auto shifting, which works great from zero because the E250 is dual turbo, so it flies from zero, perfect for Southern Cal traffic. Smode I've only used once, heavy but high speed freeway traffic while I was in a hurry, when I wanted to do some highway weaving at speed, note, also not a paddling situation, although one can paddle from Smode or Emode.