2003 GMC Yukon THE ANTIFREEZ IS ALWAY LOW AFTER I DRIVE FOR

If it's a 5.3L it may have defective heads on it. GM had heads that wept through the casting where the oil drain areas where. I had a set of those on my 2002 silverado. Although it wouldn't show up in the oil over about a month it would empty the overflow tank and a little out of the radiator. Removal of the valve covers and pressure testing is the only way to find it. If they leak GM will not warranty them, although there is a tsb out about them. I done a engine swap crate engine to be on the safe side@117,000 and it also had the heads on it. Dealer got head castings only and had to send them out to a machine shop to transfer everything from them to the new heads. The marking on them is a small parallogram under the valve train.