i got a 2004 z71 5.3 with 57,000 miles i got it new.Ive always used 10w30 castrol gtx with a acdelco or puro filter im going to switch to the pure1 scince acdelco went to ecore im runing one now and didnt know they had changed ive prob. had them on before and didnt know. ive always used gtx cause thats what my dad used and never had a problem. had a ocod lock up a honda with 30 miles on fresh oil change thats a diferent issue. im thinking on going 5w30 and staying gtx i put about 8000 miles a year on the truck and pull a boat a lot in the warm season. so im wondering what yall think stay gtx 10w30 or go 5w30 and or maybe go synthetic and if syn what kind i like castrol and also use mobil 1 in my bike