I can echo that exactly. I hated my 2.7 with the high gears. It was a stick shift, and I would usually have to downshift to 3rd gear with the motor whining at 4000 rpms to make it up hills at highway speed. I get better gas mileage with my current V6, even with larger more aggressive tires and LOTS more weight. You may regret getting the 4 cylinder, but I guarantee you won't regret getting the V6.
-Dan
Yep, I was getting 16 mpg (uncorrected) on the interstate and 14 around town and in the mountains with my 3rz with 3.58s and 32s. It couldnt pull it's own weight in 5th gear even on flat ground, at 70mph I would have to downshift to 4th due to wind drag! That was an extra 4.5" of rotational diameter though, so it is the gears fault, not the 2.7s.
Switched to a 3rd gen 4runner with the 3.4 and an auto. Same tires and wheels, and I got 19-20 on the highway and 17 around town all the time. Managed 9mpg towing a 5500 lbs boat through the hills though...it wasnt quite meant for that kind of load:sombrero:
Another thing to think about: Smoothness. The 3RZ is dead nuts reliable, simple and easy to work on, and adequate power, but is not nearly as refined as the 3.4. Many people don't care, such as myself, but the difference is drastic when you drive them back to back. The 3RZ runs like an old army truck compared to the 3.4. The 3.4 is nothing to sneeze at reliability wise either.