I have an '06 V6 2WD and I get 17.5-18 city and 20 highway. I thought it would have been better. I check mileage by hand (don't rely on the dash for calculations) every tank since new and now have about 44,000 miles. I have only broken 20 on two tanks. The first time I broke 20 was the 1st tank - so it is not a 'break-in' issue. I was babying it for break in. At that time I was real excited thinking I got 20 and it is only going to get better - NOT! The second time was at about 18000 miles.
For the record, I drive pretty hard. I have kept Mobil1 synthetic in it since 3000 miles and change oil and filter at 5000 mile intervals. From what I understand, 4WD versions get about the same since it is only a pretty minor weight penalty and you operate in 2WD mode most of the time anyway. I kind of regret not getting 4WD.
For what it is worth, in spite of the somwhat dissapointing mileage, I love my T4R and would buy one again.