Rickey beat me to it. Cold piston slap is very common in the 5.3 and is considered "normal".
P Ultra unexpectedly minimized the piston slap on start-up in my 5.3 more than other synthetics. Edge was a close second.
Thanks for all the info. Sounds like my truck is normal. Yesterday I started it after 7 days and it sounded just fine. Ticking stopped after about 30 secs.
I had a '99 Silverado that did that after 10k miles.It really has nothing to do with oil.I took it in to the dealer for it+they said it eas carbon buildup on the pistons.It only did it on startup.I took + pulled the plugs and shot some GM top engine cleaner in each cylinder,turned it oover a coulpe of times + replaced the plugs.I let it sit overnight+ the next morning VIOLA! no rattle!It came back about every 12-15k ,so I did it many times.Hope this helps!
I used to have a tick at idle in my 4.8 (couldn't hear it otherwise). Found out a particular brand of gas caused it. Switched gas stations and never had another issue. I imagine that you've tried other gasoline brands?