I did mean to say that I tested with the modem plugged directly to my PC.

It's been a few days without me updating, since I haven't had any issues after updating the firmware! My speeds have been consistent. I did change a single cable out, but all of the cables I have are CAT5 rated. 

My download speeds have once again degraded - just when through the router. I've tried rebooting and this time it didn't fix it. I've also tried disabling NAT Boost with no luck. 

Is this a hardware issue at this point?

Alright, I bought a new router from the local store because I was hoping to resolve this, but I'm have the same issue even with a brand new Archer C7 (AC1750)...

This makes me think that it isn't an issue with my wifi router but must be an ISP/Modem issue, right?!? I'm very confused.

I called my ISP and another support person took a look at it and determined the likely cause - the signal strength was fluctuating a lot and often registering at 0dB. A technician is coming on Monday to investigate further. So, the router was probably a red herring all along.

@Ohm  I'm coming to the conclusion that its definately TPLINK's issue! This is coming coming from mutiple TPLINK models.. All you have to do it google and see how easily this subject comes up

@cdh1492 

Since he/she did not follow up with what the resolution was, we do not know if it was the router or not. Unfortunately, many do not follow up. It may have been the router.

If you Google the ISP, I am sure you will have just as many hits. I have had the ISP cable issues where it was replaced three times one of which was caused by me when I nicked a cable while digging and caused all kinds of weird issues. When the soil was dry all was good. I also have had an Ethernet cable go bad, needed to upgrade my Cat 5 Ethernet cable because my service went above 100, PC settings issues, router setting issues, router location issues, a neighbor causing 'noise' on the ISP line that required a filter to be added, but never had a router or modem go bad. I still have an old unused 'G' router that works fine that must be over 20 years old. 

One of the things that stabilized/improved my network the most was when I upgraded my modem to one that had more up and down channels. Now, I have 32 Down bonded channels and 5 up as before the old modem had only 4 down channels. The old modem was at 'end of life' and I replaced it with one of the highest tier models.  

If you Google or look at the forums for any router company, you will find the same kind of issues.

TP Link and all the other router companies do have their issues. Some of the things I do not like:

• The trend for router companies to use online services to setup the router.
• Offer too many products
  • which makes it harder to for them support.
  • Harder to determine which router best fits your needs
  • lack of a compressive spread sheet of all the models features and functions
• Selling of futureware (functionality that will be added later or not)
• Removing functionality especially if not notified before hand.  
• inexperienced support.
• The lack of debuging info and tools. (especially error code meanings)

TP Link for the most part has completive pricing for the product you receive, has better web site than many of the other manufactures, has this forum with TP Link monitors, good user guides, ...

Sorry for not following up earlier! In this case, the technician said that the Coax port that feeds into the modem had a lot of blocked channels and was damaged, and he replaced it. Since then my internet has certainly been fixed, so that was the root cause for me. It was interesting how it manifested itself into a sporadic issue.

@Ohm 

Thanks for the follow up as that may help someone else.