I did a little experiment today while on the highway with cruise set at 65 mph.

At 65 mph and in 6th gear (4 cyl) the instant mpg DIC readout had me at 36 mpg.

As I approached a semi truck from behind and caught his "draft" the instant mpg went up to 44 mpg.

As I got closer, I pulled into the left lane and started passing. Immediately, the instant mpg dropped to 31 mpg and stayed there until I cleared the semi.

Once past, I changed back into the right lane and the DIC readout went back to 36mpg.

It was quite interesting to see how the wind resistance effects cars and helps understand what race cars are going through at tracks like Daytona.

Another note, at 65mph the readout was 36 mpg. At 70 mph, it was at 33mpg. Quite a difference for the extra 5 mph.

I have the same driveline and have noticed the exact same thing. I drive 60-62 mph and typically see 37 on the DIC on the flat ground. As I slowly catch up to truckers, we get REALLY good mileage :D

You should try that on a motorcycle where you can actually feel the difference. On long trips, I sometimes ride up behind a semi to get a little break from the wind.

Yeah, it saves fuel, but I'd be careful. So often, a truck will throw up a piece of debris or its own tire will fly off.