Hi Jim,
I've always used amsoil for about the past 30 years in all my vehicles. However, I wasn't pleased with some of my oil test results on my truck. I switched around a little and tried a couple of the amsoil diesel oils and the Shell Rot. 5w40 Synthetic. I consistently got better test results--lower comtaminates with the Shell than the Amsoil. Can't tell you why, but it just seems the truck likes the Shell better.
Ken
2002 2500HD duramax/allison Ext. Cab, Long bed, gray, bed rug, fumoto valve, dta running boards, peragon cover,amsoil