I know you can adjust the parameters for acc/dec and i've typically done it during any setup I've performed since they come set up shall we say piss poor from the factory. (I was a Tree distributor AE for a number of years.) Amazingly they are not protected so you can mess with them at will. Program a 4x4 square with a fast feedrate and then adjust the parameters and try again. when they are adjusted right, your machine will corner smooth as silk.
I'm a bit rusty on these since I did this in the late 90's, but may have some more info around here if you have trouble finding the system parameter.