Truck is trying to stall/hesitate when the motor is cold?
 

I've got a 1999 GMC Sierra 1500 that when the motor is cold it like wants to stall or the motor hesitates like chugs when I go to take off it does this for about 4-5 seconds than its fine for the rest of the trip tell the truck sits and the motor gets cold again. Any Idea's would be great! I have changed plug and wires.

If it is the new body 99 (both were available that year) try cleaning the throttle body. It is a very common issue on the newer 4.8, 5.3, 6.0 liter trucks.

It is a 5.3 with the newer body style, who do I clean the throttle body?

Buy a can of throttle body cleaner from your local auto parts store and remove your air intake to access the throttle body. Using the cleaner, a rag, and I also use an old toothbrush remove as much of the black carbon from the inside of the throttle body. Make sure you clean the edges of the throttle plate and the inner wall where it touches, but that cleaner cuts it pretty good so it shouldn't be hard to remove 99% of it. In some real bad cases I have removed the throttle body and cleaned it front and back. You can also remove the IAC valve and clean the tip of it and the passage where it mounts. Good luck!

are you in overdrive
if so your od might be slipping a little bit
try to drive it in drive and see if it does the same thing