I'm stumped. Please help fellow Nissan mechanics!

My X has about 150K.. many things have been done to the engine in the last year...all maint items replacement parts like timing belt, sparkplugs with wires and distrub and rotor, PCV, fuel filter, water pump, belts, hoses, all fluids changed regularly...blah blah blah....basically well taken care of outside of offroading.

Recently got back from Ouray and Moab in September, was nervous about the trip...alot of miles and offroading with a 8 year old 150k Xterra...she did beautiful.

But, two weeks later, out of the blue....my engine is "spuddering"...the best why to explain it in words. Starts perfect cold, idles great...no "spuddering" till the engine is warmed up at idle and even worse when using gas for accleration and maintaining speed. Its like the engine sounds like it is intermittently not getting enough gas. Bad gas? well, funny thing is it ran perfect with the same tank for like 150 miles before this started. Always same gas station (newer) that i have always gone to locally.

So, I changed out the fuel filter....no help, still doing it...gas looked clean and good when I let it run out the fuel line for a bit. Checked under the hood...nothing wrong externally.

So, what am I missing or what could be causing this? Engine always ran great and smooth. Still doesn't leak a trace of engine oil, no pinging...never had problems.

Bad fuel pump? mmmmm...don't know.

Sorry for the novel....

Please help! My poor X has been sitting in one spot for 2 months!

Thanks.....