The v6 has the same drivetrain as the tacoma so you get the same engine/auto trans/tcase.
The V8 has a different Tcase and a center diff to lock into 4wd from the constant awd.
We own a 05 v8 limited, love it! Gets solid mileage even lifted on 35's, and if you're a fan of the sound of a v8, ours sounds great with a magnaflow
For the extra torque, I definitely prefer the v8 over the v6 4th gen's. We get pretty similar mileage to the v6.
stock we got about 15/19 and with the lift/35's we get about 14/18. A similarly modded v6 typically gets worse mileage, i'm attribiting that to the v8 having 4.11 gearing rather than the 3.73 and then having that extra torque to lug it around.
If you go for a v8, go '05+ if possible. Thats when they upgraded the v8 to vvt-i. I might add that the 5spd auto seems to behave much better behind the v8 than it does behind the v6 even though it's the same trans- shifts at much better times and doesnt hunt around as much.