There is more than likely one of two things going on here.
There could be a lifter going bad. These tend to make a lot of noise up top, then can quiet down after the oil starts flowing and the engine warms up. This isn't an easy thing to fix, but the lifter quite readily could live the rest of the vehicles life like this without any real issues other than the noise. In order to change out the lifters in your truck, you have to have the heads pulled which is a lot of work. This is something most people could not tackle without some experience and knowledge.
You could try an engine flush to see if it might unstick the lifter, which would be the "easy fix" for this problem. Put a can of SeaFoam into your oil just prior to your next oil change. Run this for no more than 100 miles, then change (or have it changed) the oil and filter. This will get out any gum or varnish which may be causing the lifter to stick. This is well worth a try before you have lifters changed and will not hurt anything in your engine as long as you do not run it longer than the 100 miles.
The other thing it could be is an exhaust leak. These sound a lot like a lifter tap or even sometimes like a rod knock. This happens if an exhaust gasket starts to leak, then as the exhaust manifolds heat up the gap is closed and the noise disappears. To figure out if this might be the issue, look for black suit traces around the exhaust manifolds where they attach to the heads. You may not be able to see it though, if the leaks are on the bottom part underneath where the exhaust ports are.