EDIT: So I just connected directly to the modem and got fast speed test results on ALL sites. This means the problem is the wireless router. This is a new $200 router. What should I do to test and fix the problem?
Then the problem would seem to point to a WiFi environmental issue.
Start with a laptop right next to the WiFI source? Still good?
Move away and test again. Still good?
How far away is the PC from the WiFi source?