A little more info would be useful, we're not magic here!
What case, are you maxing out the fans, what rad are you running, have you checked flowrate etc etc.
Have you tried any troubleshooting steps yourself so far?
When you say thermal throttling, how far are the clocks going down?
What load does it take to get the cpu to throttle, is it doing it at idle?
Have you tried re-mounting it?