So a little bit of an update because I am a busy guy!
The 5.3 is dead, it was running really good but always had a little sound to it that I could not put my finger on since the first startup. 2k km later and a lot of drag races, it finally showed up as a failed #2 main bearing after a rather succesfull 1/8 race. Guess that's what you get for not checking the bearing condition before throwing boost at it.
The car was stuck at 10psi no matter what I did, turned out to be a too-restrictive exhaust system. So I modified an old turbosmart wastegate and put a 2" valve on it that I welded onto the downpipe. At around 1-2 psi it cracks open and let the backpressure out! It's also hooked to a vac/boost signal so it gets pulled close with vacuum. I took the idea of Nathan!
The 5.3 did a best 1/4 of 11,2 @ 120 with 10 pounds of boost,
then did 6,87@102 on the 1/8 on the run it broke for good with a decent 15 psi. It launch and pull hard, and I am still so early in the tuning process.
So I pulled the trigger on a LQ4 engine, a cast iron 6.0l that is a direct fit for my old engine. A quick disassembly to clean up the oil passage and I put it back together with a new high flow oil pump and all the other stuff I had into the 5.3.
I also opened the 4l80e pump to change and bushing in it, and also extended the rear band servo pin in it for a quicker reverse and transbrake engagement. I can't wait to drive the car again, it's been over a month now.
Power is just too easy to get with a V8 (and boost) but damn do I like it!