1994 Metro LSi Bad Milege/performance

I have been driving this car for about 2 years now. It has usually gotten mpg in the 30s in town and up around 40 on the road averaging 70mph. But recently I have been driving an hour each way to college every day, ~120 miles, and my mileage has been plummeting. I usually go 70 and not over 75 on the interstate.

Everything about the car has been performing harder recently, and the steering pops/clicks sometimes on turning.

about a year and a half ago i drove to ohio from illinois getting about 45 mpg at 70-75 the whole trip, only stopping for gas. Now my tank is on E at 170 miles and today got about 26 mpg, on all highway miles.

I just replaced the plugs which were pretty bad for gap, but the engine burns clean. Any ideas on what to check for possible problems...?

One thing i was thinking, was that I added subs and an amp recently and this could possibly be causing my alternator to be overworked. Since I crank it up on the drive home. I doubt the weight would matter, its only like 70 lbs.

Well, if it's popping and clicking on turning, it means your CV axles are bad. Bad axles can put a TON of stress and vibration on the driveline. That could be the root of your problem right there. Steering alignment could be off too. But definately replace those axles.