Rich, I've been driving the freeways much more since I discovered drafting. I'm conducting test to find how to get the best MPG. Weight, wind direction, and wind speed all play a factor in MPG. I think the A/C is not as big a factor as I thought at high speed drafting (65-75 MPH). I found my MPG dropped below what I was getting without drafting in one test. If your going against the wind but its more of a cross wind on either side, drafting behind a big truck can hurt MPG do to turbulance. I found it helped a little when I moved to the next lane away from the wind side of the truck. Weight plays a lesser role but is a factor in my test at high speeds and wind problems.

The best way I found to get the best MPG is to control your right foot. A head wind makes you press the pedal harder and more often. Weight makes you press harder on the pedal to get to the speed you want as fast as you normally would (on ramp for example). If you can't back off the pedal a big deal while drafting, its not a good draft. A good draft would be between 38-48 MPG or better at 70-75 MPH, depending on a full load to just yourself. In a cross head wind, I dropped to 27 MPG with a near full load while drafting. I backed off and got 30 MPG without drafting.

I think wind is the biggest factor in MPG for highway driving. A tail wind can really help by itself.

Wouldn't it be nice to have a gage to warn your brain that your right foot is out of MPG control? Maybe a little tone that could be turned off if you did not want to hear it.