I use Rotella 15W40. never any issues.
Amsoil is good but you got to remember that...
Amsoil is a small company with only blending facilities, they don't have refineries to produce synthetic base stock oils.. Who do they buy these pao base stock oils from???
Their major supplier of PAO base stock is Exxon/Mobil, the largest producer of synthetic oils in the world. They purchase some Group III base stocks from Shell, Petro Canada, and others. About 90% of their additive packages come from Lubrizoil.