I have run rotella in my 5.0 for 2 oil changes now with-out issue and I live in Canada were minus 25-30 over night is pretty common. Mind you I just put in a new starter which feels like it has more power than a diesel engine but I still have had zero issues. Your motor will be pretty clean after you use such oil as well and the first change comes out looking like black pen ink haha.
I've included this link from the site I mentioned in my previous post. Please take a moment to visit the link and read through it carefully.
Matthew
Whats too cold for 15w-40? - Bob Is The Oil Guy