I have had my truck in to the dealer twice for coolant leaks.
It started by having no heat, checked the coolant level and it was low, engine temp was fine. Put in a gallon to bring it back close to the correct level. It would ues a gallon in about 1,200 miles. No puddle on the garage floor, if you let it idle in the driveway for an extended period, no puddle under the truck.
First time they replaces a control valve they called a coolant control valve, $800 out of my pocket.
Second time they replaced the water pump, they warranted that repair.
It is still losing coolant, but at a lesser rate, I have put in a gallon over about 3,000 miles.
This info about the EGR leak is interesting.