When you installed the new water pump did you clean all the gasket/dirt off of the bottom mating surface super good where the oil/grime accumulates above the timing chain cover? Did you install a new water pump inlet tube as can be seen in the below link or just use the old one? Sometimes the old ones are hard to seal correctly and can leak. Also make sure your hoses are tight.
While you can't see exactly where the bottom of the pump meets the block look to see if the coolant may be coming out of the weep hole which would indicate a faulty pump.
Most likely wouldn't be a freeze out plug since they're on the sides of the block. And since the T-stat is in full view on the front of the 4.0 you should be able to see if it's leaking. Good luck.