Rodeo's if I recall had a 4.30:1 axle ratio, don't know if they are interchangeable or not.
It might be more efficient to just install a larger dia. tire, which will change your effective axle ratio.
But you're dragging around 4000 lbs of unaerodynamic box with relatively low HP, not likely to ever turn it into a mileage champ regardless. You may even get worse mpg due to the higher gear imposing more load on the engine (lugging).
You can make some gains by improving exhaust, bumping up the timing, renewing the O2 sensor, making sure your fan clutch is working properly, keeping tire pressures up, etc.
With the rising gas prices, I gave up using mine for the daily commute and picked up a Geo Metro Rollerskate. 40 MPG+ and very cheap to maintain. Plus the Trooper's not getting all worn out!
Keep On Troopin'.......ed
