Does Mcafee or any other scan you have run give you the location of theis TDSS.b!mem? If so can you post the info, it should be something like this:
c:\windows\system32\drivers\76y754Y88.sys <--Or similar
I have a similar issue. It constantly reports a TF-Downloader Trojan in what I believe is my registry. It could be a false positive, however, I feel performance is diminished, so I don't think so. Malwarebytes and SuperAntiSpyware do not pick it up. McAfee's post-scan system is hopeless, the design really is not intuitive at all, and it is not at all obvious how to remove threats. And I feel it isn't removing them anyway. If this license didn't come with my OS then I would not be using this.
I am running a scan with AVG Free to see if it picks it up. If it does then bye bye McAfee, you have served me poorly. If it doesn't it is a possible false positive.