That is an interesting thought..... You would have to relocate the speed sensor to the output of the gear vendors unit, but I don't see why it won't work other than that.... I have a feeling that you won't be able to use the OD when pulling the trailer however because the engine would loaded too much and causing a drop in mileage..... Not towing could see an increase in gas mileage at 65 MPH and higher though. I don't know where the "happy spot" is on the new 3 valve motor, but the 2001-2004 motors like to cruise at 1500-1700 RPMS (based on vacuum readings).
Matt