The 1GR-FE has plenty of power, and the Outdated 5-Speed A750F has enough gears to effortlessly propel our 5th Gens. The real problem is the Shift Points. It won't downshift unless you floor it, which defeats the while purpose of "Eco Friendly" shift points, as any time you want to get anywhere you have to floor it and dump a bunch of fuel, which wouldn't have been necessary if they programmed it to downshift sooner, and hold the gears longer.
What also sucks, is the Sport Mode doesn't make the shift points more aggressive, it just limits the high gear. If toyota was going to program such horrible shift points in "D", they should have least made the shift points in "S" better, but that costs more money...
I drive my 5th gen M-F, then my wife's GX470 on weekends. That thing has more power I could ever want, and will "throw you back in your seat" whenever you give it some throttle. It has the same, or close to the same 5-speed auto transmission. Yes it has a V8 with like 30 more torques, which helps, but what really makes the difference is that it's shift points are way more aggressive, and it holds its gears longer.
In the GX, I can be cruising at 40mph, and give it like 25% throttle, and it will instantly downshift twice (down to 3rd) and throw me back. Or just a 10% throttle application will give you a downshift, and hold it.
I can "Make" the 4runner do the same, but I have to give it more like 60%-80% throttle to get the same results. Yes you can "Learn" to drive the 5th gen better, by flooring it all of the time to try and invoke a down shift, but you shouldn't have to compensate that way just because the shift points are horrible.
All of this horrible, conservative ECU programming only nets my 5th gen 4runner 2mpg over my GX470, which also has Full Time 4wd, and a larger engine that account for that 2mpg loss over the 4runner. So a rough estimate, better shift points with in the 5th gen would only cost you about 1mpg...I would say that would be worth it!