[Ackattack]

I have a couple of buddies with supercharged/turbo charged LS1 cars running 4L60Es. They can be built to handle 600+ HP and are more efficient than the 4L80Es.

My first tank of gas through my 5.3L I got ~16.5mpg with 4.10 gears and a 4L60E. I need to do a little tuning to get better, the headers probably through the A/F ratio off a little.

All of the 5.3L have aluminum heads and most of them are iron blocks. Additionally, you can bore a 5.3L out to a 5.7L when you get around to building your forged blower motor.