New Truck - X15 Advice

[Lonestar10]

I use good ole rotella 15-40 year round and as of last oil change started using the 1 gal of gl-4 one difference i noticed is i now tend to smell the hot gear lube now and then due to 2 leaky exhaust valve stem seals. i run 15k oil changes since the truck doesnt sit. when i had 7.3l Powerstrokes i ran 5,000mile oil change intervals running the same Rotella 15-40 and never had an issue with any of them every now and then i sent a sample to blackstone labs and info i got back told me i was doing ok with those intervals.