automatic transmission stuttering

So I have an 06 coupe and noticed that when im driving and going around 38-40 mph the car will stutter and shake when accelerating slowly. I noticed that this only happens when the rpms are at around 1800. Happens more often when going up hill.

Is this normal? I believe this is when the car is switching from 3rd to 4th gear. Doesnt happen when accelerating at normal speed.

Any suggestions?
car only has 40k