hd 7790 bitcoin mining problems

[Mhash pipe]

I finally got around to upgrading my gpu from an hd 5670 to an his hd 7790. I have been able to mine ltc with no problems at ~240khash. However, when I go to mine bitcoins with guiminer, I start out at ~240mhash (default settings), and after about 20 shares, the speed drops to 650khash. I'm not sure what is going on here. I have tried just about every clock setting, but I'm afraid that my card is doing some sort of auto-throttling. The temps never get over 65ºC, and I have no voltage changes. The only flags are -v -w128, and I've got the same results on slush and btcguild. I can run guiminer-scrypt for ltc overnight and not have this happen. It only happens with btc.

Other specs:
windows 8 32bit (wasn't able to get the card recognized with xp)
catalyst 13_5 beta (wasn't able to get ltc to work with 12_10, but same thing happens with 12_10)
amd spp adk 2_8 (tried others and same results)

Does anyone know what is going on here? My 5670 would work for days straight without dropping.

[Mhash pipe]

I've been screwing with it for a while waiting for new drivers to install, and I think that removing the flags has made it not drop down. Is there a problem with vectors and the 7790? I think I read somewhere that the new architecture is good for vectors.

[Mhash pipe]

Verified that -v was causing the problem. Hope this helps anyone who is searching for a solution in the future. I wonder now if the 8xxx series will have this problem. I think the card is much happier mining litecoins.