Welcome,
The 5-speed transmission is a BRAND-NEW design. It is the new 5-speed "truck" transmission from Toyota/Lexus. It is on Toyota 4Runner V8, Lexus GX470, Toyota Land Cruiser, and Lexus LX470. Previous transmissions on these vehicles have been a 4-speed auto. The new 5-speed transmission has a nice 1st gear ratio (3.5 i think), which means that the acceleration from stop is gonna be excellent. In addition, this new 1st gear ratio helps in off-roading (greatly improves CRAWL RATIO).
How reliable is it?? I don't know. This is the first year of it. However, unlike Honda, Toyota has been well-known to make bullet-proof transmission...easily on par with GM's tranny.
The 4Runner's V6 4-speed auto tranny is similar to the "old" 4-speed tranny discussed above. It is similar to the 3rd gen transmission. However, i believe it is strengthened to match the increase torque of the new V6.
The new V8 is very similar to the Sequoia V8, but not exactly the same. The 4Runner/GX/Land Cruiser/LX470 V8 rates at 235 HP and 320 Torque, and requires PREMIUM fuel. The Sequoia/Tundra rates at 240 HP and 315 Torque, and allows for REGULAR FUEL.
Beyond these small differences, the engines are very similar. However, if you notice, all vehicles with the 4Runner's V8 (235HP/320Torque) have the SAME transfer case (full-time 4wd; aka no 2wd option) and have the NEW 5-speed automatic transmission.
Hope this helps.