Well now I'm a little confused. It sounds like you're running the power steering line through the trans cooling connections in the radiator and an external cooler for the trans. If this is the case it could be a mistake because I believe the radiator would cool the trans better than the...
If you have a clutch fan on the engine, check it to be sure that the clutch hasn't failed and the fan isn't turning as it should. In other words it won't spin at optimum speed to draw air through the radiator.