Seems like you should be in great shape having an external TBC in your path. So it's likely a PC setting. That could be a lot of possibilities, especially with Windows 10.
If you haven't already, read the
Virtualdub Capture Guide
http://www.digitalfaq.com/forum/vide...-settings.html Also search the forum. That's a very popular capture device, and I'm sure there's discussion on that topic with that device.
Aside from the capture device, Windows 10 is a very busy OS that could be causing an issue. Video capture is a real-time operation, and Windows is not a Real-Time Operating System. So, the best we can do is to try and get Windows to not be doing anything else while we are capturing. For Windows 10 that may be a tall order. An XP capture rig, as a comparison, is so much easier to start with because it's not doing as much to begin with, and it is easier to disable or kill Processes or Services that we don't want running while capturing. Try your best to disable as much as you can on Windows 10, antivirus, etc. that may be consuming CPU. Use the Task Manager and see if you notice any significant CPU activity that could be effecting things. Again, that's trickier with Windows 10 because it has so many system tasks that may be invisible in the Task Manager that you cannot control. I suppose disconnecting from the internet may help with that, as Windows 10 is probably phoning home a lot.
Another thing that has been mentioned a lot on the forum is using a separate hard drive to capture to. If possible, use a secondary hard drive for capturing files to. If it's a laptop, then you may not have that option. I don't think a USB hard drive would be ideal. A dedicated capture hard drive can help if the PC is doing other things on the main Windows Hard Drive during capture. If something else is trying to write to the hard drive while capture needs to, delays can occur, and that could cause sync issues. Best to avoid anything else trying to use the hard drive you are trying to write to during capture.
Best of luck to you.