I live in CA as well and had similar experience with using the educator discount since my wife is a teacher. I ended up ordering a truck through a dealer 2 hours away who advertised on their website they do offer/honor the educator discount. I don’t know exactly what the program is called, but the dealer sent me a screen shot that caps the rebate for the month of March as the floor for when my truck arrives middle of May. So, right now the rebate on 2021 Silverados is $4250, if the rebate is lower than that come May, GM will cover the difference. I believe the order has to be placed before the 31st of this month. Maybe they’ll continue it in April as well?
Depending on how far you’re willing to drive, I’d me more than happy to share the contact information of the dealership and sales manager I’d dealing with.