rpm's drop and sound like it is retarding ?

What is your question?

when driving around 40 mph the rpm's will drop and the car will like bog down and sound like it is retarding or something like that then if I push the gas it will kick pack in and go ? it doesn't do it all the time I will drive it one time and be fine and then I will drive it and it will do it all the ever few minutes , I changed the throttle positioning switch and it dint help