2000 GMC - 4.8 slight knocking noise

When engine is cold, I start it and it idles fine, quiet, but when I drive off -

I hear a knocking in the engine, but... after driving say 50-100 yards, it's gone.

I been told it could be a "cold piston slap"

Anyone have this same problem and how soon before I have to replace parts?

Tough to tell from this desk, maybe slap or something more serious, get a pro to listen to it.

When engine is cold, I start it and it idles fine, quiet, but when I drive off -

I hear a knocking in the engine, but... after driving say 50-100 yards, it's gone.

I been told it could be a "cold piston slap"

Anyone have this same problem and how soon before I have to replace parts?

Like Maxwedge said, it's hard to determine without hearing the noise for ourselves.
But, in most cases this may be a cold carbon knock (some people call it piston slap, but there is a difference)
When the engine is cold, the carbon deposits on top the piston are hard, when the engine is started, the hard carbon hits the head and causes the knocking sound you hear.
I own a 02 GMC and it does the same thing, usually you can let the engine sit and idle for about 2 minutes before you drive off and you will not hear the noise.
I have over 90K on my engine with no parts replaced..I have customers with 300K on thier trucks with no ill effects.

The idea of carbon deposits on top the piston makes sense to me.

Is there anything I can buy that will remove the hard carbon, maybe special oil?

Thanks for your help!