Ultimately, I solved the issue by buying a TP-Link Archer USB WiFi Adapter. Also, two weeks ago, I bought a new Linksys dual band router.
I am getting a rock solid 150 Mbps connection on my system with 5.0 Ghz network, and I am connecting to Comcast at about 109 Mbps with 100 Mbps service.
The odd thing is, my TP-Link USB WiFi Adapter seems to be rock steady at 150 Mbps.
Placing my old Toshiba laptop in the same spot, the adapter will report varying connection speeds between 100 Mbps and 200 Mbps on the same 5.0 Ghz network.
What gives? My desktop won't go above 150 Mbps but never goes below, either. Doesn't fluctuate at all.