1996 SC2 Power Loss

I have a 96 Sc2, 2 weeks ago i was driving on the highway when i felt what seemed to be the wind blowing straight into the car. Then I went to the place i was going and got back in and the car had kind of a drag to it. the next couple of days it got worse it would go to 3500 rpm and not go any higher. i disconnected the EGR valve and it runs a slight bit better but stilll lost RPMs and Speed going up a hill on the highway at about 65 or 70 down to 55. I replaced the O2 sensors and still dont know what could be wrong with it.