@RDhero 

A few things to try:

• If only WIFI drops, change WIFI channels and width
• Check to see if any devices are eating your bandwidth such as cloud backups.
• If you router and modem have logs, check them for errors.
• If you are paying for above 100 and it drops to 100 or slightly less, try new cables.
• Check the MAC addresses to ensure you do not have any unwanted devices.
• Do a longer test with the PC direct to the modem since if starts out fine and drops.
• Turn off VPN if you are using one.
• Isolate each device to ensure you do not have a device causing the issues

@RDhero 

Some things you mention do not add up, at least to me?

RDhero wrote

I had no internet which is the reason the tech was there (isp router burnt up).

First, was it a modem, modem/router combo, or ISP router that failed? I'll am not sure because of other comments?

RDhero wrote

So with the new passwords and wireless name there was nothing on the internet except the hardwired computer.

OK, makes sense if the ISP replaced a ROUTER for you? So is this an ISP owned A10?

If it is your A10, then why was there new passwords and SSID name?

What does this have to do with the original subject of "Fast at First then Slow"?

RDhero wrote

 When I plug the net directly from the POE to the computer it gets normal speeds.

I'll assume 'POE' is "Point Of Entry"? Do you mean a wall connector for Ethernet?

Now what do you get when you take that same connection, put it into a LAN port on the A10 (which I assume you own), and then a cable from A10 to the 'wall' or 'modem'?

RDhero wrote

The bottleneck or issue is the router in some capacity.

Well, maybe, but maybe not?

Usually when you add a device or router to a modem that was already working with a different router or device, you need to power cycle the modem and device or router, with the modem powered up fully first. I'll assume since you used POE (as I understand it to be) you might NOT have access to the modem to do that.

Now since you said you have full speed when a PC is connected to the POE, please try CHANGING the MAC Address on the A10 to be that of the PC that got full speed and test. That would be done on the A10 GUI under Advanced, Network, Internet, MAC close setting.

@IrvSp my apologies. The Poe (power over Ethernet) helps power the line of site dish. And the router from the isp was a router only, I replaced it with the a10. The router from the isp went bad before I replaced it. The tech came over to remove the router, I had not set up the a10 before this point and decided to do so once the tech told me it was not in fact a modem.

When I plug the Ethernet from the dish directly into the a10 instead of through the Poe, I get no net being the dish no longer is powered. 
 

when hooked up and working, my net will run as it should, then on the same speed tester (Ookla) it slows to about 50% of previous speeds on the second and third tests. I then switch ports to say 3 from 2, it again runs great then slows down. 
 

I believe this article covers what I'm exp

https://community.tp-link.com/us/home/forum/topic/153101?page=1

@RDhero,

Read part of the link. Different router, older too, with no real resolution.

If you've not contacted support, I'd do that for this one, see https://www.tp-link.com/us/support/contact-technical-support/

@IrvSp ok thank you