2001 Elantra automatic shifting trouble

I have a 2001 Elantra that seems to hesitate between gears.
It is just taking longer between gears than it should.
It does not happen all the time.
I had the speed sensor changed about 8 months ago for another trouble.
Also have changed the transmission fluid twice.
Is there a sensor that controls the shifting that could be bad?
Any ideas before we take it to the shop?