[azraelswrd]

I would drive at the most efficient speed for that truck, regardless of the semi's and if possible, stick to the slow lane. Avoid fast followers and follow someone at your speed and you should be ahead of the MPG curve.

The problem in trying to keep up with a fast semi is that you might be using more gas to accelerate/maintain that speed than you will save on the drag reduction. Without a scangauge you won't really be able to tell for sure if you are making any savings until your next refill.

Also comes the question of drafting -- how close/far would you have to be to get any real benefit at those speeds? If it means moving to "death" range (ie 0-2 seconds behind them) the risk of injury/damage is not worth it plus it is illegal in some jurisdictions.

Figure out your truck's fuel efficiency sweet spot (best speed @ lowest rpm in highest gear) and work around that -- at least that's what I would do.