@redfitz 

Since it is both Ethernet and wifi, I would suspect the Macbook. 
 

Use your OS utilities to see if you can isolate the issue. Start with the activity monitor. 
 

Also do the usual things like power cycle, reviewing disk space, memory usage, check security, ...

  @ArcherC8 Thanks. However, nothing looks amiss in Activity Monitor. Nothing else is sending any data of any significance at all on the Network and there's plenty of memory and CPU bandwidth. I also have had no problems utilizing full upload bandwidth on other networks with this MacBook Pro.

  @ArcherC8 

To add to this, I just tested uploading using the same MacBook Pro on an identical TP-Link router in a different location and achieved virtually the same upload speeds as those reported by the router via a speed test. On that router I'm getting around 40 Mb/s which is basically what I'm paying for. And on that one, I'm much further away from the router and separated by several walls. Whereas on the router in question, I continue to get a max of 27 Mb/s despite the router speed testing at 513.7 Mbps.