D15 is the minimum air cooler for a 9590. I would not get anything else for air.
And, be sure to have a fan blowing onto the VRM sink. Put a fan behind your motherboard socket, too. It doesn't have to be as powerful but there is some extra cooling to be gained from doing that with an ASUS board. A 120mm slim sleeve fan would be fine.
Ignore the advice about replacing the CPU.
The good news is that you have a very good board that will support that CPU fine.
The other issue could be that your RAM is causing trouble. AMD FX is only rated for 1600 speed RAM with 32 GB and 4 sticks as far as I know. You may need to drop your RAM speed and tweak until stable. But, I bet your problems lie elsewhere. 1600 RAM at CAS 9 doesn't really bottleneck (although CAS 8 is better) because of the large cache on the FX chip. I didn't notice much of an improvement from switching from CAS 8-8-8 1600 to CAS 9-11-10 2133.