So part of the reason I can get a whopping 15 mpg city with my Durango (sometimes) is that I have a few hills that I can coast down for nearly 5 miles. I've noticed though that the rpm's when coasting are at 1500 instead of the normal idle rpm. What gives?

I was thinking that maybe there is a vacuum leak somewhere but I don't know that much about this transmission so I thought I would post here to see if anyone might know.

I have the electronically controlled transmission.

 

Are you in drive or neutral while coasting down the hills?
FF

 

Forgot to mention, Neutral.

 

I believe that is correct behavior, as this is what mine does, seems like a grade retard action by the transmission. On really long downhills, it keeps the speed down without using brakes.
Dave

 

I could accept that if it weren't for the fact that it is in neutral. Maybe the firmware for the transmission isn't that robust. Is there a way to "tune" the transmission?