Arrgh! Hate it when the computer behaves that way, not just because it's irritating that it won't work but because finding the solution can easily suck hours out of a day, with little progress.

-do you have antivirus software running? if you temporarily disable it, does the problem persist?
-if you turn off the router or internet, does it still happen?

My first thought was that you have some sort of adware or malware running constantly in the background, which is tying up the cpu, thus causing skipping or jolting of other programs, but you indicate that the cpu usage is okay? Are the rest of the programs you're running slow as well (ie. lag time between text typed and when it appears)?