Hey Phil, I agree with the 14-15 mpg, as I get about 16-17 combined right now and plan the same mods as you. I noticed the biggest difference when I switched from the 265 stock tires to the 285 BFG a/t's.
I echo your sentiments on 4 wheel parts, and had a very poor experience in San Marcos. The counter jock actually referred to my Xterra as "a grocery getting soccer mom vehicle." I promptly returned my purchase and went up the street to ORW. Haven't been back since.
Glad to see you are realizing the pluses of the Xterra. I too did a lot of research on these great vehicles, and came away impressed, even more so now that I own one.
AND....a great community of owners!
