2000 Ford Ranger sudden engine rev up

The problem is when I go to slow down or stop the engine will rev up and if I put it in gear and slowly let out on the clutch it will stop or return to normal idle. Also when I am driving and go to switch gears it stays revved up while switching gears. It doesn't happen all the time but it does happen often. So far I have replaced the throttle position sensor, and the idle air control valve. I was going to see what else you think it could be.