02Escapemanual

Hey, so i have a 2002 ford escape 2.0L xls 4 cylinder Manual and i've been having a problem as of late. my car idles perfectly (500-1000 rpm) starts everytime, engages in gear everytime without slippage, but my problem is whenever i try to accelerate the car struggles in each gear. I will have the gas pedal to the floor and the car will accelerate but its seems like it is choking out and will take a long long time to reach any speed. My first gear fully stretched out usually gets me to 50 km/h but now, fully stretched my car only gets to about 20-25 km/h. its struggles going up hills and i can barely get to 100km/h to be on the highway. I've changed the fuel filter and even brought the car to the mechanic where he said it was a weak timing belt. i paid for that to be fixed and the problem did not go away. (i installed the fuel filter my self). do any of you have any suggestions as to what the problem may be? ive exhasuted all my limited car knowledge and i can't search on google for problems anymore. HELP!!!