I did a shitload of driving this past week...I went to Princeton last Tuesday for a friends mom's funeral, Thursday to Baltimore to get another friend coming in from MN, then drove to CT Friday, drove home Saturday and back to Baltimore to drop my buddy off at the airport.
I didn't use the cruise control like I normally do and my MPG's didn't drop like they did before using it. I was getting about 23MPG and I topped out on the way home Saturday at 24 MPG going by the computer.
The big thing I've found is to keep the RPM's low and apply the gas in a "pulse", which is basically accelerate to speed, let go of the gas so it downshifts and then apply very little gas to keep it at the speed you want (I was doing 75-80)