First off you will find that there are only a couple options when it comes to R&P's for the VX. Secondly these gear sets are very rare and hard to find. Unless you are running a different size tire I doubt if you will see a significant change in MPG.
You say you are only 2 wheel drive? Have you disconected the TOD? Removed your front drive shaft? Manual front hubs? If none of this has been, then you are not 2 wheel drive (unless you have an imported JDM model). When not in 4lo the TOD splits torque between rear and front as needed when wheel slippage is sensed.