2001 blazer rpm going crazy

This problem usually occurs on wet days but is getting more frequent. While driving the rpm will jump from 1500 to 3500 causing the tranny to downshift and the whole car jumps. On the highway when accel the engine will jump to almost redline and the tranny will not down shift to help pick up speed. When car is put in park the rpm again jumps to 35-4500 and holds until i turn off engine. Sometimes a hard rev will make them drop. When the engine restarts if it has not cooled off they go right back up. Cleaned tb as well as changed the throttle pos. sens. nothing helped. Any feedback would be great thanks