Yes its Gm,
they have always been crooks when it comes to parts.
When you say Zr1 they laugh all the way to the bank.
They will wack you close to 800 for a fuel pump when it is common knowledge you can you a 96 Surburban pump $100 give or take.
I was a Gm tech for 7 years, I know the way they think and the way they train their employees. Not customer centric.
Ray