new to my 04.5 dmax and was wondering what oil to start using. i've done 2 changes so far and used 15w40 valvoline premimum blue( which is what a buddy uses in his cummins, w/ no problems) and ac delco filters. i go 5k between changes. i guess i could go farther between changes if i used synthetic? was also wondering if it would be safe to go to 5w30. i do some heavier hauling during the summer pulling loaded haywagons and other farm eq. i know during the colder months the 5w would be ok. in my gasser i always used synthetic and it was great. we also use synthetic in my dads vw tdi w/ well over 100k and its great in that.just wondering about the dmax and what everyone uses. thanks in advance jim