I am experiencing the same problem as of last month. it could be the "winter gas".

as a matter of fact I replaced the OEM tires with the same 265/70R REVO's before I noticed the fuel consumption increase.

I also cleaned the MAF, replaced the AMSOIL, reset the EFI and I will try to replace the plugs tomorrow.

the fuel filter is located right about underneath your butt, you can't miss it if you look under hte car.

w.