The popping is most likely your steering stops, nothing to worry about. Just grease them, put new caps on them, or just live with it.
There's not much you can do about the lack of power and mileage with the 3.0. I hear exhaust helps, but I'm skeptical.
It's possible to get the trd locker in the rear, but you have to remove the whole axle and do some minor welding and drilling. Here's more info:
http://www.4x4wire.com/toyota/tech/electric_locker/
Alternatively, you can get an ARB or detroit in there without difficulty.