Loosing coolant slowly

[chainsaw]

I can see a small coolant puddle after my truck sits for a while. The coolant drips from the front of the transmission - the area between the oil pan and torque converter. I park the truck in my driveway which is on a severe incline and the transmission is the lowest point on the truck. The sides of the engine block are dry as best as I can tell. I looked at the egr coolers and they look dry. A visual inspection from the top of the engine does show any coolant leaks. The driver’s side motor mount is a little damp with engine oil – it definitely is not antifreeze.
I rented a radiator cap tester. I pressurized the system to 15 PSI and after 45 minutes, the pressure dropped to 13 PSI. I had to quit because a storm moved in. I had driven the truck for 20 minutes so the engine was warm but to super hot. Where should I be looking for the coolant leak?

[BeauxPete]

from what I have read and experienced it sounds like the upper radiator hose leak that alot of us have dealt with. It would be the first place I looked.