USB ports randomly stop working during high system load

I've been googleing and searching the forums here to no avail for days now.

Basically, the problem is that while running some 3D games, which I assume are taxing the system more, as well as generating heat from the CPU/GPUs, all of my USB ports, 2.0 and 3.0, on the motherboard (back panel) and the case (front panel), will periodically stop working. First, the mouse will start hanging, becoming non-responsive for less than a second. After a couple minutes of that, the mouse will hand for a couple seconds at a time, and the Windows PNP device "unplug" and "plug" sounds will play. Next, the mouse will become permanently non-responsive, quickly followed by the keyboard, printer and USB mic. When these devices turn completely non-responsive, the only thing I have found that will remedy the situation is to restart the system. This has never failed to work, but the period of time before this problem starts happening again seems to be greater from a cold start than a reset.

At first I assumed that this must be a driver problem, so I updated all of my drivers and mobo firmware. I also check my power settings, and disabled USB selective disconnect. Then I went into the device manager and checked the power settings for each usb device and the root hubs to make sure that windows couldn't turn them off to save power. None of this helped.

Next I assumed that it must be a motherboard problem, perhaps a defective USB controller that was overheating way too easily. My motherboard was only a few months old, and still under warranty, so I got it replaced. At first I thought this had fixed it, but after about 45 minutes the problem was back.

The only other thing I can think of is that my PSU could be defective, as it is the oldest component in my system at about 2 or 3 years old, but I wanted to get another opinion or two before I got and drop $150 on a new one. Below is a list of my hardware, and thanks for any help.

ASUS Sabertooth Z77 mobo
Intel i7 3770K cpu
4x4Gb Corsair Vengeance DDR3-1600
120Gb SSD
1TB HDD
2xEVGA GTX 670s, SLI
1000W PSU, can't remember the manufacturer, as I said somewhat older than the rest of the system and as I recall I didn't pay too much for it.
4x120mm case fans
1x140mm case fan
Corsair H80 CPU liquid cooling

USB Peripherals:
hp Inkjet printer
Logitech HD400 gaming mouse
Microsoft Natural Ergo keyboard
Logitech USB mic