To the OP: When you had your wheels powder coated, did they cover the inside area of the wheel where it contacts the wheel hub? If so, remove any paint/powder coat on this contact point - it's preventing the rotor/hub from transferring heat to the wheel to dissapate.
I had a similar issue this past summer, going through 3 sets of rotors in 3 months and going crazy trying to figure out the cause, until we narrowed it down to my OEM front wheels which had been refinished over the prior winter... the wheel shop had painted over the contact surface resulting in both a really tight fit to the hub, and also preventing adequate heat dissapation from the rotors to the wheel. The SA at the dealer carefully removed the paint from the contact surface and no issues since (it's been over 6 months).
May not be your issue, but worth a look.