Raising the CO value greatly improved my bike!
 

This mod took 2 minutes, and has dramatically improved throttle response. I don't have to downshift as much anymore, and the jerkiness coming on the gas out of corners is GONE.

The mod is a piece of cake. The stock value for my bike was 6, and I raised it to 16. I very highly recommend it as a first step to make any stock XT660 run better.