While you have your rad out, remove your water pump and make sure your divider plate is no more than 1/16 inch from the impellor blades. Use a hammer to beat into place(while removed from pump, of course). Trial and error...you'll figure it out.

I don't buy into the cast vs. stamped blade comparison. I use a Flow-Kooler pump with 8 shrouded stamped blades. It has worked well for over a year.