Don't rely on the overhead console, they're not as accurate as we would like them to be. I always calculate mine by hand, and for best results, you should keep a mileage log so you can look for long term trends.
Oddly enough, I've found that ULSD doesn't make a huge difference on my 2nd Gen 2wd 12 valve. But then again, I'm pretty mellow on the throttle. I'm still getting 20 to 21 mpg, and I attribute the decline in MPG to lack of use more than the fuel. I don't drive it very much these days.
It's a good idea to check all the maintenance items regularly. Also, for 4wd, check to make sure your front universals and bearings are good. I have one coworker with a Ford, and his mileage dropped about 4 mpg. Turns out to be a bad wheel bearing; he did his u-joints and balljoints while he had it apart.
Eddie