In keeping with the title of this thread I have one more bitch to add. AFM otherwise known as Active Fuel Management that is in older Yukon 1500 XL Denali's with a 6.2L and other engines. It constantly shifts between 8 cyl and 4 cyl. GM's smartass engineers claim it saves up to 12% in gas however owners report saving 1 mile per gallon. It causes lifter failure, higher oil consumption and the problems I had with the truck hesitating, shuddering and nearly stalling out while driving less than 50mph.