What up guys. I'm having trouble with my 2.0 zetec. First of all it has a very SLOW accleration.What could be the problem???

Just started about a month ago. When you are running along at about 45 to 50 mph and you press the gas, you almost have to push it to the floor to make the engine drop into a lower gear. When you do this a funny burning rubbery smell comes though the vents when A/C or fan is on. I've asked around and have recieved many different "could be" problems. I just added a Y-pipe to the exhaust system, and had the EGR valve and the epcf ( i think that's the name of the sensor) sensor changed. ANY suggestions appreciated!!! PLEASE!!!!
