I have a 2002 dakota with a 3.55 axel ratio . I have no plans to carry or pull heavy loads at this time . I would like to know the expected MPG improvement if it where changed to lets say 3.23 or maybe the next smaller number . I would like to also know an average expected price to buy and install the new rear gear . Is it difficult to reverse the procedure if I wish later to pull a small camper. It has a 3.9 motor and auto transmission