Hello. My problem is similar to the one above:

(1992 Dodge Shadow mileage: 84k. My aunts car... You will be driving along on the highway when all of the sudden your speed will start dropping from say 65 all the way down to say 20 mph. If you push on the accelerator, it doesn't do a thing it just sounds like you are revving up the engine. It will last that way for quite awhile, and usually you have to pull over because of the speed decrease. Then all the sudden it will be okay again...)

My symptoms are the same. I took it to two repair shops who both recommended replacing the catalytic converter. I did, but three weeks later the same problem occured. Thanks!