Update: back to the dealer today for an intercooler bleed... good news and bad news.
The good news is there was a lot of air in the system, so I'm hopeful the problem has been fixed.
The bad news is dealer service people are idiots, and
never listen to the customer...
When I made the appointment, I
specifically asked if they had the service tool to bleed the ZL1 system. I even
specifically pointed out it was unique, and different from the ZO6 tool. The service manager even went in the back and asked (what he asked, I don't know...). He told me they were good to go.
Of course, I bring the car in and they don't have the tool...
Now, I didn't know any of this until I picked up the car... Turns out they installed a ZO6 bleed fitting, because they had the tool to bleed it. Of course, it doesn't fit properly, and puts a bend in the hose that shouldn't be there. So now I have to go back
again after they get the tool, so they can re-install the original fitting...
Why GM would use two completely different bleed fittings on the LT4 in ZL1 vs. the ZO6 is completely beyond me. What a f*cking PITA.