Got a 2002 Xterra, stock size tires, any options to help with gas mileage maybe a little taller and a little narrower, any suggestions??

There were 3 stock sizes on the 02 Xterra, care to elaborate on what you have now?

Don't go narrower.

There were 3 stock sizes on the 02 Xterra, care to elaborate on what you have now?

Don't go narrower.

P265/70 R16, I thought maybe a little taller would gear down some, and a little narrower would be less drag thus saving MPG, mostly highway driving
V6 auto

Taller, 265/75-16 is the way to go. Narrower compromises your grip/handling far more than it might save in fuel. A harder compound, and raising the pressure up a little, will go further towards mileage.