Right,Ron! There are a load of variables.I was only saying that if you want optimum gas mileage,do the mileage check with ALL grades ,`cause it's a great indicator of the torque received per BTU input.The more torque,the less gas you need to give it,thereby,putting it in simple terms,the less gas goes thru your injectors or carb into your engine for that mile of travel per that speed.I have a 460 c.i.d. engine in my F-250 that just wastes gas constantly because of low rear-end gearing.I'm thinking I'm gonna sacrifice a little of the heavy-dutiness of the C-6 tranny and opt for an AOD out of the lighter built F-150.If I'm careful I think it will last and give me a lot better gas mileage.The point of saying all this? The 460 HAS the torque,(BOY,does it have torque)so I'll be letting off the gas quite a bit.