Answer: Typically if this is a Chevy 1/2 or 3/4 ton two wheel drive with 373 or better rear gears you should get 10-12 mpg. If this has dual wheels and 410 or higher you might get 7-9 possibly 10 if you got the wind to your back and are on the decline of a really steep hill.
Answer: The expression is: Do not teach your grandmother to suck eggs. It means Do not presume to instruct an adept. In the days before toothpaste, flossing and dentures were common, many elders had no teeth. Toothless grannies all knew perfectly well how to suck an egg for nourishment.
Answer: Granny gear is a term used for truck manual transmissions extremely low first gear.This type of transmission would be one that when driving normally around town you would start out in second gear.the very low gear reduction of the first gear would be used for low speed pulling or crawling where the extra torque is needed.
ANS 2 - Granny gear is also used in bicycles. On any bike with three chainrings, the smallest, innermost ring is often referred to as the"granny", or the bailout gear. Having to drop to the smallest chainring is often seen as the last resort before having to get off and push the bike, if the incline gets too steep for any of the "regular" gears.