Your leak sounds like the same issue I am fighting with on my '06 GP with 3800 Series 3 engine. It is leakinging on the back side of the engine above the power-steering pump. Here is a list of things I have changed so far: Upper intake gasket, lower intake gaskets, water-pump, belt tensioner plastic lines to the updated alluminum lines.
I fill the system with coolant, bleed it, and it will start leaking as soon as the engine is running and while cooling down. I have checked around the tensioner tubes, clear around the water-pump, and they are bone dry, as are all of the hoses. Coolant runs out on the back side of the engine running off the oil filter housing and in that area like a rain forest. It will leak until the resevoir empties.
I can't really see anything on the back side of the engine, but would like a few ideas before I start tearing the thing apart again, or pulling the engine.
My gut tells me it is coming from the rear head, is there anything else back there that has coolant in it?
