Upon cold start ups and once I put the transmission in gear out of park, a rattle starts coming from somewhere in the general area of the passenger side valve cover. The rattle gets faster as I give it throttle; it disappears relatively quickly, by the time I'm out of my neighborhood its gone.

What do you all guys think it could be? Anything would greatly appreciated.

 

Timing chain getting loose usually sounds like a sewing machine and will not go away. I'd guess it is in the exhaust system since it goes away when the truck warms up.

 

Thanks for the suggestion, makes sense.

Anybody else; there has got to be more of you that can help me.

 

Look for broken exhaust manifold studs in the head. Pretty common.