Replace transmission cooler???

[Sasquatch]

OK a quick update, I think I have all of the external leaks stopped on my truck, and I appreciate all of the info. But now I am loosing coolant internally in the engine. As best I can tell I am not getting any coolant into the oil, and the truck isn't running hot. But it seems that I am steaming the coolant thru the stack, and the engine seems to be blowing pressure back up thru the coolant reservoir. Some I'm guessing head gasket, injector seal or bowl??? Not really sure, but I kind of need to know how to determine the real issue, and about what to expect for cost on these various repairs, so strapped financially, and still paying for this circus ride.lol.
Any guidance is appreciated.