OCCT is a much better stress tester than P95, I find OCCT will find errors much quicker than P95.
Also to do a proper stabilty test you'll need to run it for 24hrs! (don't run the Linpack version, that one's just stupid! lol). That obviously covers cpu,mbrd & RAM, as far as testing the GPU though I haven't found any one test that will tes them conclusively. You could do a mixture of OCCT, 3dmark, & games testing, which is reckoned to be the best testing you can do.
Btw re drivers, are you sure the previous (newer) drivers have been completely cleared out?