Lemon laws vary between states, but in my case (NC) you have to give the manufacturer the opportunity to fix the problem after notifying them of the impending intent to use that law. That's where we are now, it's just taking too darn long.
In defense of GM, they likely don't have any spare engines laying around, and so it does need to be scheduled into production, and that can be challenging.
The upside of threatening to sue under a lemon law is that you will make corporate aware of the issue, and if the OP is so inclined, might institute a buyback.