I've use Amsoil in my engines for about 7 years now and have been happy with it. I had Mobile 1 in the rear axle of my '92 Z71 because I ran across a sale just before I got ready to order Amsoil. My current 2500hd has Amsoil (light blue color to match my Airstream believe it or not) rear end gear oil and I run Amsoil 5w-30 in the crankcase. When I run across a sale on Mobile 1 5W-30 then I have purchased it but I opt for the Amsoil most of the time. Amsoil ATF has been on the market for years and since I am not familiar with a Mobile 1 ATF, I stay with Amsoil. Other companies producing synthetic products are Royal Purple and Red Line not to mention the oil companies who are handling synblends. All of them are better than regular oil particularly under extreme conditions or extended intervals.
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system