[bigmike]

Before you tear into the motor, listen to my saga.....
I have the hottest 428 around, or at least had the hottest.
Typically, I would boil over in traffic and run about 220 to 230 on the freeway...very frustrating!!
I added a rubber air dam all around the radiator to seal the nose air intake to force all of the air through the radiator. Guess what? I dropped a solid 40 degrees in all modes. 175 to 185 on the freeway, and 200-220 on the street, in 100 degree weather. I was amazed at the change. Might not be your problem, but certainly worth a try.
BigMike