I don't know for sure and I can't say for sure, but I would doubt that GM would switch to a twin turbo just to get even with Ford. GM's VGT (Variable Geometry Turbo) works better than a twin turbo setup, even one with two different sized turbos. Ford only switched to twin turbo 'cus (I think it's) International Harvester pulled the Navistar contract for the Powerstrokes, or the contract ran out. Anyway, the GM/Isuzu Duramax has all the joint work on the computer controlled turbo and Ford would have had to start from scratch, easy way out: two turbos. GM > Ford IMO