I had a question about MDS. I heard that when you engage the tow/haul or o/d off modes, it disables the MDS. I’ve done this for the past year, but when I slow down or coast, occasionally I'll hear a noise from the exhaust that sounds almost like a Jake brake on diesel engines. I do have an exhaust cutout, and I never heard it before I got the cutout, and I only hear it in tow/haul or o/d off mode. I assumed this was the MDS engaging, because as soon as I tap the gas, it goes away. Recently, I download the Superchips update with the MDS delete option. When I drive around without tow/haul or o/d off on, it seems like it works and I don’t hear anything like the MDS turning on. But, when I drive with tow/haul or o/d off engaged I still hear the same sound when slowing down or coasting. I was wondering if this noise is the MDS or not, because it is annoying when I’m driving and I hear whatever this noise is, but I like the shift points in tow/haul mode much better, and I like the sound of the cutout the rest of the time.

 

Someone far more knowledgeable than me will answer, but I think you are hearing the tranny downshift to slow the truck. Part of the tow/haul function I believe.

 

Yup, I agree. It's the tranny downshifting. The common word for it (and it's incorrect because it's a tranny function) is "engine braking", it's the downshift of the tranny to slow the vehicle to save the brake pads from the heat build-up of braking with a heavy load.
Coast down a hill with the tow/haul off, then coast down the same hill, at the same speed with it enabled. You'll feel abrupt downshifts while in the tow/haul mode.
Another situation where this is beneficial is going downhill in snowy, icy conditions where applying the brakes (even ABS brakes) could cause you to lose control of the vehicle. With "engine braking", you could maintain better control...

 

I have to disagree. Engine braking in snowy or icy conditions is never reccomended nor can be beneficial when you are in a 2wd or 2wd mode as it would be similar to stopping with your emergency brake. Slide out can and will occur. Engine braking is only beneficial when you are in 4x4 mode. If you are in 2wd the only axle that would be slowing you down at that point would be your rear axle which has the least traction. With touching the brakes, you will at least have 4 wheels stopping you.
The correct way would either be using the engine brake in dry weather for 2wd vehicle or in bad weather with 4x4 vehicles as all 4 wheels will slow down the vehicle.
Another way to go down a rather steep hill with 4wd if you have no engine brake would be 4-Lo. Your gearing and your engine will maintain a super slow pace for you and will allow you to go down very steep grades without ever touching your brakes. Actually you'll prob have to press your gas because it will slow you right to a crawl.

Being in trucking for a few years, the use of engine brakes in bad weather has always been a no-no since the tractors are only driven by the rear axles and not the steer axles.

A gasoline engine will never have and engine brake since most are in the valves and use compression to slow the speed down. Some diesels use exhausts, but the valves are the better more effective way. The downshifting is only the transmission Tow/haul mode which is nothing other than what it seems. The tranny downshifts to help slow you down because you are in tow/haul mode so generally that function is used when you have weight being pulled behind you. This function helps when you don't have trailer brakes. It saves your pas and can be much safer to use it than without.