Engine RPM revs up right before shifting (automatic transmission)

I had the timing belt replaced over the weekend, and after that I noticed the RPMs go up slightly right before shifting. It never did this before. Right before going to the higher gear you hear the engine rev up and RPM jump up by 400 to 500, then the car will shift and RPMs go down to normal. It will do this on the next gear and so on.
The mechanic replaced the timing belt along with water pump. He pulled a lot of parts out of the way to get to the belt. Could he have forgot to put something back or messed up something while doing all this.