Your vehicle speed is read off your axle, so changing your differential won't affect it, changing the tires will.

 

No computer update needed on a gear change.Mds comes on any time a lite or no load.Mine might come on creeping through a subdivision or at 80 mph on the interstate.Do make sure the latest/greatest FLASH update is done on your truck.Idle quality,shift quality etc.is addressed.

 

Make sure you ask the person that quoted you the gear change if it includes the limited slip (posi-traction) carrier. Would not want you to go thru this and still be unhappy because you still ended up with a one wheeler peeler with 3.92's!!!

 

if you are talking about 09's , my MDS comes on at low mph and over 70... I have seen it ... I have the 321's and love the truck ... i drive a lot of miles 3,000- to 4,000 a month

 

YES! when it says "eco" your in 4 cyl. fuel saver mode!