I was thinking about changing to Shaeffer's Supreme 9000 5w40 since that's what I ran in my 7.3L for years. However, it appears that both the Shaeffer and Motorcraft are made from similar base stocks, so I'm not sure the Supreme 9000 is superior enough over the Motorcraft syn to justify paying to do my own change.
I am still getting free changes on my truck, had the 2nd change at 11,000 miles, and was considering doing another now at 15k miles.
Until the free changes run out, I think I may stay with the Motorcraft full syn 5w40, then will probably change to the Amsoil Premium 5w40 Diesel Oil since I know that is a minimum Base 4 stock, as opposed to the above mentioned 2 that are both Base 3 hydrocracked/Base 4 blends, which can be called full synthetic.
Last winter, the truck started fine at -24* with the Motorcraft syn.