Title says most of it: my data editor is lagging. Whenever I change any value, it starts lagging for 2-3 seconds EVERY TIME. My cursor blinks between the pointer and the circular W7 loading symbol repeatedly, then it stops and the lag ends. In that time, I cannot do anything else, and it's a big waste of my time (say 500 values *3 seconds; 25 minutes). Any idea what might be causing this? (This issue occurs on any map)

It also has all the campaign and story mode (under the "object family") units in it; any way to get rid of them?

The editor processes some data. With my computer I only have to wait half a second (2*2.5 ghz, 4 gig Ram) whenever I change a value. But selecting a unit in the list takes much more time for me.

-Close modules that you do not need. Just having the Terrain module opened uses up to 9% of my CPU.

-Trying to reduce the included files could improve it. Under File > Dependencies, you can modify the dependency.
Maybe that helps.

Other possible improvements:
-defrag your files (e.g. with a program like defraggler)
-disable autostart programs that you do not need (execute msconfig.exe)

Open your task manager, change a value and have a look at the CPU usage during that 3 seconds.

Even on faster systems it tends to give a second of lag. I think it may have something to do with how it updates the value, it changes it and then reloads the data automatically. Even on my 2*3.0ghz sys, I still get a second or two of lag.

As for how to make it faster, Ahil nailed it pretty much, don't use unneeded dependencies, try to only keep open modules you are actively loading, and do basic maintenance on your system to keep it running smoothly.

If single player units are showing up, you should be able to remove them from the dependencies (File -> Dependencies), just click on the two campaign modules one at a time and hit Delete. If it says they can't be deleted due to being in use, move them to the bottom of the list (highlight them and hit the down until the Multiplayer ones are above both of them), hit OK. This will reset dependencies to base off of the multiplayer mods. Then re-open the menu, and then delete the campaign modules.

I'm pretty sure this happens similarly to the World Editor for WC3.

Great! Got rid of the campaign units, Thx!
As for the lag, When I change a value, my cpu usage goes to 11%. W/o doing anything, the editor uses 15% of my ram. The lag is really quite annoying; it wasn't lagging like this 3 days ago, and I must have changed over 200 values...
My comp specs:
i7 1.6ghz (quad core)
4gb ddr3
Geforce gts 360m (1gb gddr5)
I think 5400rpm HD (500gb)

Edit: after getting rid of campaign units/dependencies, it now takes about .2 seconds after changing a value (from 3 seconds).

Yeah, the higher the amount of data to search through, the longer its going to take to update, especially if you factor in sorting and searching. I believe adding in the campaign dependencies increase the units count from somewhere around 150 to 750, and that's just units. With a standard sort algorithm, that would increase time to refresh the list by about 700%, so it easily adds up.