Which oil for 2003 Silverado 6.0L

[Yukon_2A_FTW]

New to the forum
I have a 2003 chevy silverado ss lq9 6.0 with 203k miles. 4l80e awd. Has kooks long tube headers/full exhaust. Truck runs great. No oil loss between services. Oil pan is very lightly wet but not dripping. Oil pressure is 35psi at warm idle with current mobil 1 5w30 high mileage . I live in alaska where it gets -40f give or take in winter and 80f give or take in summer. Truck is daily driver and idles a bit in winter and summer occasionally does some short wot pulls. I've looked and looked and get tons of conflicting info on what oil I should use. Should i use the mobil 1 5w30 high mileage full synthetic or change to something like Mobil 1 FS 0W-40 for cold factor and summer pulls? Gets oil changed late fall and early spring. Im sure im over thinking it lol.
Thanks

 

[fantastic]

0w-30 ESP or that 0w-40 ESP would be good

 

[PontiacHO]

Whatever it’s had for 23 years has done the job. Carry on.

 

[CleanSump]

current mobil 1 5w30 high mileage

And Bob is your uncle. Unless you want to go to 0W-X for the -40F cranking. If you've had no problems with Winter starts, there's no need to change to a 0W-30/40 and if you're not consuming oil, no need for the -40 as a bandaid.
Maybe consider the current darling Valvoline Restore and Protect 5W-30 if you do have consumption to see if it's dirty rings that can be cleaned up.

 

[melk]

Nice engine. M1 ESP 0w30 is a great choice

 

[Kira]

A 2003 "Alaska truck" with 203k miles!
A picture or two sure would be appreciated.

 

[BrendanC]

Mobil 1 0w-40 would be my pick. i run HPL 5w-40 in my 6.0 in Texas. keep the oil changed and that 6.0 will go on forever. i have 247k miles and 12,000 engine hours. still runs like a top and drive it everywhere.

 

[SwampSurvivor]

I'd stick with whatever got it to 200k miles.

 

[BrendanC]

I'd stick with whatever got it to 200k miles.

a non AFM LS will make 200k miles with cooking oil in the sump. doesn’t mean there aren’t better options for the same cost.

 

[fantastic]

A 2003 "Alaska truck" with 203k miles!
A picture or two sure would be appreciated.

Maybe not a good idea.

 

[Snagglefoot]

I have a 2008 6.0 closing in on 300,000 miles. Runs well. An oil analysis reveals some cam bearing wear which is normal. I went to a 5W40 for the summer but for cold weather in Alaska I would use a 0W40. What I actually do is run 0W30 in the winter and 5W40 in the summer.