Like Bush said, you could be overfilling it, make sure you don't fill it up past the MIN on the bottle. It's also possible that you have an EGR related issue, or absolute worstcase (and unlikely unless you're running some HOT tunes) it could be a headgasket issue.
I'd clean the bottle off, and keep a close eye on it, to see if you can pinpoint what conditions it is causing it to "puke" out the coolant, like were you towing, heavy acceleration, steep climb, etc....
If it continues to happen, after verifying appropriate coolant level, you should get your dealer to look at it, if it's still under warranty.
Also fill out your signature, with your trucks info, so we can better help you in the future.