It will depend on how the truck is used.
If towing they will be more, unloaded with the RPM's below 2000 I can see 5 or down.
My truck I have the RPM above 2000 all the time, 4.88's are the reason.
So mine is a little more than others with a 250 and 3.73's.
After the truck is warmed up on the road I am in the 3-7 range.
Towing I have seen around 13.
I dont see how it can be 5 for every truck all the time.
The CEL would be on all the time for me.
When i first start out, the difference is the same, then it splits some till the thermostats open.
Then the difference can jump some because of the coolant from the radiator.
Now it comes back together again and stays pretty consistant from that point.