OK, hope someone has some suggestions as to what I should tell the dealer and how long to gather data before calling them

The fuel pump on my diesel went out on the 23rd at 4500 miles. Got it back last Friday. Prior to replacement, I had gotten between 24-26 mpg combined on every tank tracked through mileage and actual gallons bought. I keep a book in the glove box and figure the mileage manually after every fill up. Im a mileage whore most of the time. Like to see how high I can get it when I'm not having fun on good roads.

Since replacement, Ive noticed the X not only feels a little sluggish, but also struggles to get 20mpg average. I might chalk the perceived sluggishness up to getting used to a 335i as a loaner for the week, but Ive been driving with a lighter foot than normal and cant move the computerized mileage gage past 20. It seems like the instant mileage meter goes lower upon acceleration. For instance, very light acceleration will bottom it out past 12mpg on the meter. Any idea what could cause this? Should I tell the dealer now or wait to burn through a couple tanks and see where it stands?

In addition, I had just filled up the day before the pump blew, so I know how much fuel it had and the mileage. While it was at the dealer for repairs, it went through almost a qtr tank and had 80 miles put on it. When I dropped it off, the computer was showing its normal 25 mpg. When I picked it up - 18.2. There was also mud on the carpet and door sill of the right rear that I know for a fact wasnt there before.

Has anyone had the service dept go on what looks like an extended joyride while your vehicle was in the shop? Could this have anything to do with the mileage drop? How many miles would they have to run to test the new fuel pump?

Thanks for your help.