Correct answers
This is definitely a WiFi problem.
From what I've seen, Macbooks often are smart enough to switch over to the faster, less crowded 5 GHz band. Sometimes PCs struggle between connecting to 2.4 GHz (an older, slower WiFI band), and 5 GHz.
If you recall from your old Comcast setup, you probably had two networks. One probably looked like MY-NETWORK, and the other was MY-NETWORK-5G.
Verizon routers on the other hand combine both 2.4 and 5 GHz networks into one name, and its up to the device to pick which band it connects too.
I'd suggest you add a -5G network, and force your Dell to connect to that, and then re-do speed tests. Heres how to do that:
Login to your router at the following address: http://192.168.1.1/
The username / password is on a sticker on the side of the router.
Click Wireless Settings on the top bar.
You should see a status page.
Now, in the left bar, click "Basic Security Settings".
You should now see a page as follows:
In the text box titled 5 GHz SSID: add -5G to your network name, like so:
Lastly, scroll down and click "Apply".
You should now see the new -5G network on your device. Connect to that, and forget the old network on your device.
Re-run speed tests, and see if you still have the issue. When testing speed, make sure you are using the official Verizon speedtest (https://www.verizon.com/speedtest/) to get the most accurate results.