I gave it a try in my 2006 ISX, but I kept getting spikes in lead and a few other issues, so I gave up on it. I have been using Schaeffer for a while now. The cost is very competitive with Wally World pricing and it is shipped for free to your front door. And if you get 55 gal drum amount (which I do) you get free oil sample kits and analysis thrown in the deal. I have been using a 15w40 synthetic blend they have with good results, but I want better cold weather flow since I stay in the upper midwest year round, so I am considering their 5w40 full synthetic. Just talked with my rep and they want $669 for a 30 gallon drum, shipped free. Amsoil's preferred pricing on their 5w40 synthetic is $801.00 and you still have to pay for shipping. Schaeffer is the oldest oil and lube manufacturer in N. America, since 1839. They make very good products. You don't see them on regular retail shelves since that is not their main market. They cater to commercial users. They developed the lubes for the Apache Attack helicopter and the Abrams M1 tank. Get an idea that they might know what they are doing?
I don't sell it, only use it. You have to go thru a commercial field rep to get the stuff. They will set you up with a commercial account and ship free on orders over $375. I am fond of their fuel additive and their grease is fantastic. If you want more info, give Dan Dykema, my rep, a call or send him a note.
Schaeffer Oil | Dan Dykema - Sully, IA - Oil, Grease & Specialized Lubricants
You can find all the technical data sheets on their products here....
Schaeffer Oil | MSDS, Technical Data Engine Oil, Lubricants, Fuel Additive, Grease Sheets
Technical data sheet on their 5w40 synthetic....
http://www.schaefferoil.com/documents/244-9000-td.pdf