You may have some blow by that is burning a little oil, check your exhaust during a cold start to see if you blow out any blue smoke. The 5.3 is a pretty tight motor so it shouldn't be burning much oil (if any). The 8.1 vortecs burn 1qt or more between changes so I wouln't be too worried about 1/2qt, just try to check your motor once you're under there next time for any leaks for the main seals.