Q: Driver Loss in Windows 8 Upgrade

Apps and drivers are a different and unrelated issue. For Drivers, are you using BC drivers, or have you allowed Windows Update to update your drivers?

Is Windows Update enabled for Automatic Updates?

Windows Update may have drivers to update, which do not work the same as BC drivers provided by Apple. Unfortunately, Apple's driver are not in WHQL, so it is a bit of hit and miss if the drivers for generic cards get applied to an Apple variant of the same card. I disable all Automatic updates, but will check each update before I let it be applied.

For the BC drivers, one option to consider is to download W8.1 drivers from System requirements to install Windows on your Mac via Boot Camp - Apple Support and Boot Camp: Install or repair Boot Camp drivers.