You could change any of the parameters (rear end gear, tires, speedo gears adapters etc) just depends on what you want to do long run on the build as in are you keeping stock period correct tire sizes. and your budget.
You could do a 3.50 or 3.73 rear end gear change out.
if you do it just changes the needs of the speedo gears.
going from a 15 now to a 17 tooth or 18 tooth respectively.
So in the end you are changing something on the gear speedos unless you get to a 3.90 or 4.11 rear end which is going the opposite of where you want to go.
if your desire is to keep the good highway and milage performance.
rebuild or repair your rear end. Leave it at 3.07 and get the gear adapter 1.30 (three on ebay at moment) and you will be closest.
