Do you have the "Color unknown object messages" option turned on?
That option can affect script editor performance. If it's on, try turning it off and see what happens.
If that's not it, can you give us some more details on the problem?
Does the typing problem happen with an empty script editor?
How many lines is the script that is scrolling poorly? Do you have lots of JMP windows open or just the script editor?
-Jeff
-Jeff