outdoorav,
THe 6.0 will idle itself up in cold weather to try to get the engine temps up. If it is really cold, it weally wont warm up. I have drived mine in teen temperatures 20 miles on the interstate and it does not get ot normal operatin temp. I do need to get a winter front though..... There is also a "High Idle" mod you can do that uses the PTO control to run the engine at 1250rpm at the flip of a switch, I have not doen this either.
One thing with the 6.0 is you do not want to idle them for extended periods of time as it will cause the EGR Valve to soot up and not work correctly.