That’s not your problem since Vegas Pro V10 does NOT support GPU for effects processing. AFAIK, V10 only supports GPU rendering using the Sony AVC format If this is what you are using for renders, simply open the render dialog box, select the custom button which will bring up the Customs Settings-Sony AVC window. In the very bottom under Encode mode, select using CPU only.
If this doesn’t solve your problem, you will need to provide detailed information about the media you are using (screenshot from MediaInfo), Project Settings and Render Settings (screenshots). All in all, it seems highly unlikely that your problem has anything to do with GPU.
wwaag