Once I get above around 40 miles an hour or so, any sligest acceleration seems to cause my truch to shift in and out of different gears or so it seems like the transmission is shifting. Even when I run over a bump the truck races or shifts.
Would this be the Throttle Position Sensor and if so how big of a job is it to change it?

 

sounds like a kickdown cable in need of adjustment

 

Thanks JD770, but what is a kickdown cable?

 

cable that runs from the thottle body down to the tranny. also called a detent cable. You cant miss it, look at your thorttle body(carb), you will have 2 cables(maybe 3) one goes to the gas peddle, one goes to the tranny, and one goes to the cruise unite, not all will have this one. Do a search on here and you will find info on how to adjust it. Its not hard and doesnt take to long. good luck