Poor Gas mileage?.......Differential possibly to blame?
 

A few months ago I had my diff inspected/rebuilt by a local transmission shop while I had my subframe out replacing bushings and what not. I got it back and noticed a) there was a slight whine while in gear b) it seemed to be much more responsive, often chirping the tires under seemingly minimal acceleration.

Fast forward....I've made several long trips and have noticed a drop off in fuel economy. Whereas before I could squeeze 350mi out of a tank, I now struggle to hit 275. (I have installed an Rtek and cleaned my injectors as well, but the AFR's haven't changed so it couldn't be running significantly richer)

How do I know something is wrong?.....I took the ole' girl out sliding (or attempting to) and a slight blip of the throttle would kick the ass out turning left. However nothing (even 4k clutch kicks) would make her break loose when turning right. Leading me to believe that the extra "responsiveness" I felt was pass side of the diff being always locked. As it seems the driver side is perpeturally open....a conclusino supported by tread wear analysis ;) and some scary moments rolling onto the throttle @ 70 in the rain (stock turbo mind you...)

So my question is this; can an improperly assembled diff cause a significant decrease in mpg's? What about a worn diff?

I can see the extra friction created by the gears being too tight or what not causing you to use more fuel. The engine has to overcome this friction which = more fuel.

Your diff shouldn't whine. Whine = Bad.

Also, if they put a bigger ring gear in the diff, your acceleration would increase, your fuel mileage will decrease.