Extreme Power Loss

I have a 91 Explorer and it now has a problem of not wanting to go above 1200 rpm even when I have the pedal floored. It has been about 15 degrees where I live, and I was told that it was probably fuel line freeze up. I changed the fuel filter (not fun when its 10 degrees outside!), put some dry gas in, filled the tank to about 3/4, and tried started on a day when it was 30 degrees, but I still have the problem. I haven't had any problems of it not starting or of it stalling. It just hardly has any power. I'm thinking maybe it could be the mass-air flow sensor. Any advice is greatly appreciated.