I don't know off hand,that tranny is pretty new,and I haven't got much info on it yet.
If it's similar to the older Dodge's,then it probably won't have much cooler flow in park.
I wouldn't be too concerned about it.It isn't a problem on the older trucks for warm up.The only thing you shouldn't do is to throw it in park when the tranny is hot (after towing,or pushing snow),as you get very little cooler flow.The only time I would use neutral when first starting,is if the truck has been parked for a long period of time,to help fill the convertor and cooler lines.