That vacuum line from the valve cover to the TB is going to be a bad deal. I did the same thing with that TB. It never really acted up when I had the 4.8 because the cam was pretty large which created little to no vacuum at idle. But once I put the 5.3 in with the same cam my idle vacuum came up and it developed this god awful squealing sound at idle. I dealt with it for a bit because of the zero fooks given with the motor. I ran it for a month or so making this squealing sounds at low idle.
It bothered some else enough for them to look at it. It was the oil fill cap. That hose was creating enough vacuum that I almost couldn't remove the oil fill cap with the engine running. Amazingly it never sucked a crap load of oil in nor caused a seal/gasket to get sucked in.
In a nutshell, don't start it up like that. Unhook the hose and let it dangle and plug the port on the TB. You should put that hose to either a catch can or pre throttle plate source. I say **** emissions and don't suck oil back into your motor. I made my hose longer and stuck behind the water pump. My motor is tight enough that it doesn't blow anything out at 20+lbs of boost, but I should have it hooked to a catch can.
Also, what is your throttle cable and let me know how it works - I probably need to address cable at some point as well.