I'm at 85k and I just:

Changed my diff fluid
Changed my transmission fluid
Cleaned and re-oiled my K&N filter

The car feels smoother, quicker, and all around much better however my fuel mileage has declined significantly, from 23 miles per gallon to 19.7 miles per gallon.

I haven't been driving more aggressively, and I've been doing essentially the same mix of city/freeway driving.

The only other thing I've noticed now that I never noticed before is the smell of my exhaust from time to time, which makes me think the car is running too rich.

Any ideas?

 

May want to check and clean your maf sensor. It is a possibility it is getting faulty readings if some of the excess oil from the filter found its way onto the maf. I would assume you used recommended oil for the diff and trans.

 

I did use recommended oil for both trans and diff. I will have a look at my maf sensor and see.