Good Monrning Cartech,
I have a 2012 FX35, just hitting 55k miles. Car has been completly reliable, absolutly no issues since new. Other than replaceing tires once and wiper blades several times, all I've done is routine maintenance. We happen to live over 100 miles from the nearest Infiniti dealer, so all my service work has been done at our local Nissan dealer.
Last year did a road trip over 3,300 miles. We managed to put our FX through the gambit of wind, rain, altitude, temperatures, and speeds. We traveled from the extreme northwestern corner of WA down through OR, ID, to Salt Lake City UT, and then on to St. George UT. Leaving St. George, we headed South to Gold Canyon, AZ, via Valley of Fire in NV, and then headed home back up through AZ, NV, ID, OR, and finally WA. We experienced travel from sea level to over 8k. There were a lot of our travels at elevations exceeding 5k feet. We went from 0 MPH in a couple of construction zones to some (short) cruising at 100 MPH in the Nevada desert on the long straight stretches of Hwy 93 (FX really sucks gas at that speed!). Most of the time we ran at about 80/85, and we were loaded down with luggage and on the return, adult beverages (much cheaper in NV/AZ than in WA, about half price!). Many of the highways (ID, NV, UT) are posted at 75 and 80 (Utah), and you can pretty safely run at 5 to 10 over. We hit severe headwinds for a stretch in NV that absolutely killed our fuel mileage (dropped to 18) but overall average for the entire trip was 21.3 MPG. The FX performed flawlessly, was a real joy to drive, and quite comfortable, although at about 6k feet in elevation, it was noticeably working harder. Hope this helps. Would I buy another FX, without hesitation!