Improving Gas Milage

For a big car, my 2000 MGM with 70,000 miles has been getting impressive gas milage compared to others of its size: up to 30MPG highway (with slight wind in my favor :)). But now that it's winter and milage drops, I'm looking for a way to save a few dollars at the pumps for the long hauls between campus and home.

I've been reading around and doing some research but I am by no means a mechanic or even realted to one twice-removed (well maybe I am but not that I know of).

Here's some precautions I take now for fuel efficiency:

I have my tires inflated to the maximum psi as indicated on the tires (44psi front, 35psi rear).
Oil is changed regularly every 3,000 miles using 5W-20.
Body is kept clean to reduce skin friction drag (I'm a pilot, I love me some aerodynamics :)).
Cruise control is used when possible on the highway.
I don't usually drive aggressively, although that doesn't always apply.
Keep the weight down as much as possible (usually just 1 or 2 people in the car plus a little baggage).
Usually do between 65-70 on the highway which I found to be the sweet spot for best milage.
Has a new fuel filter as of 5,000 miles ago.
Used STP fuel injector cleaner gasoline additive back in November.One other thing I was looking into was purchasing a K&N air filter to improve air flow. For $60, would it be worth it? Would it even make a difference for this car?

So what other things do you suggest? Anything I can do with the engine to increase milage without decreasing horsepower, maybe even increasing horsepower?

Well upon further research, I found that the K&N air filters aren't all they're cracked up to be. And going for longevity of the car, it would be in my best interests to just stick with the paper filters.

So any other suggestions?

First, air the tires up to what is on the plaquard on the door pillar. More than likely either 32 or 35 psi front and rear.
Has it been tuned up lately? That might help some.
Winter warm ups use a lot of fuel, so there is nothing to do about the weather unless you park in a heated garage.

Actually, I was looking for the recommended tire pressures in both the owner's manual and the plackard on the door. The door did not seem to list them (atleast not plainly written), and the owner's manual said to inflate to the pressure indicated on the tires.

The car has been in the shop about a month ago. It had an oil change, new brakes put on, and the power steering fluid flushed. A few months ago, I had all new spark plugs put in and the induction system flushed.

As far as I know, the transmission fluid was never flushed (it's at 70,800 miles). I check all fluids about every month when I visit home for a weekend and the transmission fluid level is fine, but I'm not sure of what the texture of clean transmission fluid is.

I don't think tranny fluid would affect gas milage anyway, but I should have modified the title because I'm also interested in making this car last me through college (another 2 and a half years) and beyond and keep its great performance and smooth ride. So any maintenance suggestion you may also have to keep this car going strong, that'd be helpful too.