I did an experiment like this a while back with a 318ti, 5spd. Try this - instead of using CC - just 'lock' your foot angle into the same spot. So get up to about 55mph, if that's the speed you'll be cruising at, and keep it there. Nevermind you may decrease in speed going up an incline. If you go up - you will go down, so your speed will naturally increase. Try not to brake if possible and pop it in Neutral any chance you get (even if you have an automatic) : Coast to stop lights and when moving into the exit lane to get off the highway.

In a car that was originally designed to get a max of 29 MPGs highway, I was averaging 33.1 MPGs.

But because CC will vary your throttle position to maintain your speed, it doesn't really give you max performance. Maintaining the throttle position is what will get you MAX mpgs.

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2006 X5 3.0L - Schwarz Black/Truffle Brown
Stock
But I keep it clean