XPS 15 9560 very slow after sleep mode - stuck at low CPU clock speed

Bought a fully-loaded XPS 15 9560 about 3-4 weeks ago and am having issues w/ CPU clock speed, specifically after returning from sleep mode. It will get stuck at a particular ceiling and won't throttle higher, and performance is terrible. A reboot makes the problem go away. Frustrating, as I don't reboot often and like to keep applications running/open while working on several projects, simultaneously.

I'm having a hard time re-creating the issue consistently. It seems to happen most often when I let the PC sleep overnight and return to use it the next morning. I just tried triggering it by going into/back from sleep mode, both plugged and unplugged, and could not make it happen. I did have the problem this morning after leaving it in sleep overnight.

All drivers are up to date, as well as BIOS. I ran the full Dell Diagnostics and everything passed. No malware or viruses, and all unnecessary background services are disabled. It absolutely screams when running properly, after a reboot...no issues otherwise. I'd just prefer not to have to shut it down after every session.

Here's a good description, though I'm not able to re-create the issue the way this person was:

http://en.community.dell.com/support-forums/laptop/f/3518/t/19660225

I contacted support but received a very Level 1 Support response (malware, too many background services, etc.) - nothing helpful yet. Will continue w/ them as well.

Any help would be appreciated, thanks!