It's not too far fetched to have a transmission cooling tank leak inside the right hand expansion tank of the radiator. A simple pressure test could bare this out. It can't be an intake leak as the intake is bolted on the side of a four cylinder motor.
It might be a bad head gasket. If the pump is still leaking, you might have pinched the gasket upon installation or you need to tighten the bolts a bit more. Did you change the hoses as well? The old ones may have torn when you removed them from the old pump. Good luck.