You dont need a 4L80e (good idea though) but you will need a well built 4L65e minimum, I have a FLT level 5 and it is holding up fine, 7000 miles on it now (knock wood).
Use the search function and read up. Click my sig and go to page 2. There's a ton of info here.

 

I had one and liked it. But there is a certain point where it does become restrictive and you need to step up to something bigger

 

Is that Country, or Western? I can never tell the difference.

 

It's a drinking song, gotta be country.

 

alright then ill look in to a 4L80e. i know of a place where i can get a 1000hp rating 4L80e for around 3 grand and it comes with a kit so it will fit onto the 5.3.

 

The Radix is a great blower, but if your concerned about running on the hwy with a turbo don't be. Anything above 20 mph on my setup and the boost hits instantly. From 20-50 mph if I go wot the tires go up in smoke. If you get a gt-60 and a 2600-2800 stall there will be little lag if any.

 

On the STS you can also wrap the pipe from the motor to the turbo and it will spool up alot faster. In one case TRT told me that they were reaching full boost at 2500 rpm.

 

if you do put an 80e in, rememeber, you will need to modify your crossmember and buy a new driveshaft.

 

I think I'm gonna ditch my procharger for an MP122 w/ my new engine.

 

That song is Awful, Beautiful Life by Darryl Worley