If your hash rate is dropping every few minutes, then your problem is with bad values for P7 and P3 (OverDriveNTool), or too aggressive settings in XMR-STAK config file.
What do you mean by "bad values"? I get hash speed drops within a couple of minutes on my Vegas.
Also, I cannot for the life of me get the powerplaysoftmod working for some reason. I noticed that the reg file spit out by OverdriveNTool was slightly different (different number of rows/columns) compared to the reg files posted in the Overclock.net thread. The files posted in the overclock thread allow me to boot into Windows but as soon as I try XMR, it crashes, but it works fine with Eth mining. The files spit out by OverdriveNTool more often than not causes Windows to not boot, so I have to boot into safe mode, load the stock reg file, then reboot, back to square one.
Anyone can provide me with some advice on what to try? I'm only doing this because OverdriveNTool is not allowing me to change voltages, only clocks. Running blockchain driver on a Vega 56 and 64, and currently using MSI Afterburner to change voltages since it actually works.