Starts fine, dies during warmup, runs good once warm.

2005 6.0, got it 14 months ago it had 208,000 km now has 260,000 km. ran perfect till late last summer. starts great at any temp but dies during warmup.
It would start fine but if i left it idling it would die after a bit, then die a couple miles down the road. Wouldn't start up for five to ten minutes then it would all of sudden just fire up like nothing had ever been wrong, do that a couple to three times but once it got warm enough it would run all day no problem. As the weather got colder it would have a harder time getting thru the warmup stage. Dieing more times and taking longer to fire. Changed the ficm, did egr delete, new batteries, it didn't change a thing other than that I haven't been able to use it for the last couple months because its so cold it can't get warmed up. Any ideas? I'm ready for my truck back.