I have a 2001 Silverado 1500 z71 w/ the 5.3 in it... it has 151,000 on it and is burning about 1 1/2 qts of oil every 2500 miles. There is no smoke when I start it or drive it and there is no oil on the driveway. my engine is clean and has no leaks. I ran Castrol GTX and then Castol High Mileage to see if it would make a difference. I have looked around on the internet and chevrolet might have a service bulletin on it. Could someone help me out or point me in the right direction?

Thanks in advance

 

ttt

 

Have you checked the radiator for oily water?