uh wow, good thing I read this thread. After checking my mining rig I noticed a significant decrease in hash rate as well. Thanks
You don't need to unibstall the old drivers. Just go into Radeon settings and enable Compute mode for each GPU.
And run the pixel patcher.
Also, what he said is right. Didnt even need to change to compute (dont have relive anyways). Just had to un install and re install patches from pixel patcher and reset afterburner.