Video has a mild stutter, streaming and some local files

My new video card is an nvidia GEFORCE GT 730 GPU (2gb DDR3 RAM) on a Gigabyte PCI-e x16 3.0 card. I'm using the HDMI output on the card to an HP Pavilion 22bw LED monitor. I've tried two other HDMI cables and a DVI cable to see if the cable or port was at issue. The nvidia driver is up to date. The monitor does not have speakers, so I'm using the onboard Realtek audio. I've disabled the HD audio via HDMI, but it didn't make any difference compared to having it enabled. I installed this card a couple of weeks ago.

My motherboard is a Gigabyte GA-Z77-DS3H, about three years old. I used to use the onboard graphics (Intel Graphics 4000 HD) through an HDMI cable. Results were the same, or very nearly so.

Do you still have the drivers for the iGPU installed? Can you try the following:
Install LAVFilters, open LAV Video Configuration, choose Intel QuickSync with all the tickable boxes ticked, and tick Hardware Deinterlacing 50p/60p (Video).

Then try again and see if that improves anything.

The iGPU drivers are no longer installed; I removed them when I added the nvidia card and reduced video RAM available to minimum in the BIOS so I could use the full 8 gb of RAM.

I did install LAVFilters, though. I chose nvidia with all the boxes checked and chose Hardware Deinterlacing at 50p/60p, but it didn't make any difference. I rebooted before streaming again, but the problem remains. I don't know if LAVFilters can help otherwise, but I'll see what I can find out.

Update: I had the thought to try running a couple of problem videos through Windows apps instead of a browser, and they play smoothly with the apps.

I may be wrong, but this tells me that the problem isn't in my hardware or drivers, but in the browser and/or Flash, HTML5, Silverlight, or whatever is being used to run the streams in the browser.

In doing further research, I found that some, perhaps all, of the streaming services send out their streams at 23.976 fps, and it seems that my PC is set for 29.97 fps. I know that that the shows I via PlayOn are recorded at 29.97, even coming from sources that I know stream at the lower rate. Could this be the issue?