Hey guys I just found this website a few days ago. So far I am very impressed with all the knowledge and information on here. I am trying to soak up as much of it as I can. I am originally from Texas and am living here for a few years so this cold weather is kind of different for me. I know some of the basics about oil weight kinda. The lower the W the more it flows right. But I am not sure how exactly the second number affects the oil temperature rating. I currently driving a 2004 GMC Sierra 1500 with the 5.3l with 68975 miles on it.It was a safety supervisors truck so it saw alot of hiway miles and some extra idleing. The oil was changed fairly regularly it looks to me. Right now I have Quaker State peak performance 5w30 in it. I am wanting to go with one of the heavy duty oils like the Delo 400 syn 5W-40. It calls for a 5w30 though I think this will be okay right? Would you recommend this or something else?