First off... l I'd ditch the Lucas. Oil viscosity effects mpg. Hence ford secs 5w20 in their 4.6 here but in and there's countries they call for 10w40. Lucas doesn't really do anything great. Want to maximize your mpg through oil... run a decent synthetic. Mobil 1 can be had on sale for 35$.

I wouldn't dare put that stuff in your diffs. Its not gl5 rated. It's not capable of handling the high shock of of direct contact gears. A lot of what lucas says isnt verified or true. See bobistheoilguy.com for the facts.

Maybe simple maintenance... change all your fluids and filters, a quick check of your alignment (tape measure will do), check air in tires, quick clean of the air flow meter is applicable, and check the drive line for resistance (wheel bearing play, drive shaft u joints...)