Low power engine

We have a 2002 Toyota Camry, the problem that we're having is when the car is cruzing at 55 to 60 miles per hour the car boggs down an doesn't allow you to go any faster. Now we would like to keep up with the traffic. We have taken it to the mechanic which he checked the computer, both 02 sensors, checked the catylitic converters, spark plugs, changed serpentine belt and we're still having an excelleration problem. The mechanic stated after cleaning the throttle body, that the problem could be the excellerator peddle sensor. We need your help now, Please!