How many miles are on your truck? I'd let it break in with about 5k and re-evaluate your mileage. Some people on here seem to start out from their first mile on their truck with decent mileage. My story is a little different though. I have a Dec built truck from St. Louis and do have the MDS light. My initial mileage was less than desirable. I was getting 10 avg city and 15 avg highway. I even took it in to have the dealer look at it. They didn't find any fault codes. I knew to expect lower mileage for initial break in, but I still thought this was too low. I figured I would give it a chance to break in more before pursuing it further. Sure enough, I just recently crossed the 5k mark on a long road trip. Over time it has been gradually improving. I am now at the averages advertised on the sticker and beyond. Not sure if you may be seeing something similar to me, but if you are low on miles, break it in some more before you panic.

 

Mine has the light, but it's not really needed. You can feel and hear when it kicks in, even with the stock exhaust.

 

I couldn't hear mine with the stock single exhaust, but I could feel it.

 

Tell me should the rpms drop when it kicks it or increase on the highway lets say around 80KM/h

 

I do notice that at certain speeds it doesn't have the guts to hold the speed and either starts slowing the truck down or if you compensate with the pedal it goes back to all 8.

 

it doesnt drop on mine, I can hear a slight change in the exhaust but it is minimal and would have to be listening for it..

 

There's only about 1,200 miles on the truck right now. When I started to check the mileage it only had about 300 miles on it and averaged it on a 600 mile trip. I hope mine is like yours and gets better with break in.

 

RPMS's will increase ever so slightly when MDS kicks in. That's because the convertor will unlock a bit and allow more slip ro reduce driveline vibrations.

 

With my rigged MDS light, I can tell when it is on, which is next to never. 3.92's, 8000 miles on truck. I am going to have it serviced soon, I know it needs a PCM reflash for the rough idle. I have an Oct 08 truck.