Try these parameters:
--gpu-platform 0 -d 0 --no-submit-stale --thread-concurrency 10048 --intensity 17 --worksize 256 -g 1
If those parameters do not work and you have the same 20khs, you need to wipe your driver platform clean using the CPanel add/remove program Catalyst uninstaller program.
I highly recommend the Cat. 13.4 / 2.9 SDK combination. 12.6/12.8 + 2.9 should be fine as well.