Thats turbo lag my friend...
It's completely normal. Turbo lag is the time required to change power output in response to a throttle change, noticed as a hesitation or slowed throttle response when accelerating from idle as compared to a naturally aspirated engine. This is due to the time needed for the exhaust system and turbocharger to generate the required boost. Inertia, friction, and compressor load are the primary contributors to turbo lag.
The 6.0s lag really isn't all that bad. Drive a 7.3 or a cummins and you'll experience some real lag. As for making it a bit better off the line I would get a FICM Tune. Look on FICMRepair.com and it explains it all really well. A 4" free flowing exhaust will eliminate any back pressure and also help a little. Custom tuning can change some parameters and help as well.
Do a little more reading on here and you'll find a wealth of knowledge on the subject. If you really wan to take off the line try practicing a brake stand. It's not exactly good for your drivetrain but the truck will take off a lot faster. Or if your desperate for a super quick jump off the line try a boosted 4x4 launch. On a tuned truck you'll be thrown back into your seat! The truck will take off like a bullet.