I think it really depends on the speeds you normally drive and what type of truck you have. At 75mpg, stick your hand out the window, there is significant drag force. It *can* make a large or little difference.

Frank.

1994 4runner, 3.0, auto, 4.88's, 31's, BJ spacers, Coil spacers, air shocks, D-ring anchors, 4Crawler F/R swaybar discos.
www.sdori.com