Did you look here what others achieved?
Did you check marketplace?
Why not 24 months? The payment will look much better with the same discount and rebates.
Also, it will not be easy, but try to find 24MY demo unit. It gets an additional $2500 as a rebate.
GM EV products are all about rebates, so the deal with the same dealer discount can be great or bad.
Do you have Costco? Lyriq had $1k rebate by end of February.
What about Polestar 3? Or MB EQE? Are you open for a different car?
