VERY low upload speeds for past few days

I will try direct connection, thanks.  I use a Synology 2600 router.  Didn't know 6141 was only approved for 100Mbps, I have generally gotten 175/7 (down/up) with it.

I wanted to get a signal issue taken care of before pushing Cox to provision my 8200 (since I didn't want to give them something else to blame). Had a tech come and fix low signal issue, but then things got busy and provisioning the 8200 got put on the back burner (still on the to-do list, 8200 just sitting in the corner collecting dust).  Thanks for the reminder!

I have generally gotten 175/7 (down/up) with it.

Hmm, maybe you need a modem with more tuners for the full 250Mbps. Either way, upload is the problem, not download so probably not relevant.

What is an NIU?  I have an entrance point box that was used for my prior copper land-line phone service (Verizon) and a smaller Cox cable entry point box, both on the side of my house.  Will read through that thread, thanks,

Maybe I read your post wrong. Only glanced through it.

What is an NIU?

NIU is Network Interface Unit. It was for Cox's older circuit switch technology before they changed to eMTA for VOIP. See post here for more info.

a smaller Cox cable entry point box

Is that where your demarc is with your splitters to split the signal to other outlets in your house? Also, any problems with TV service like issues with OnDemand?

Overall I would suggest bypassing the router first and see if your upload speed returns. If not, try bypassing the splitters in your house with a coupler to see if that corrects the issue. If not, you need a technician.

Okay, bypassed the router and got 215/0.40 speed, so better download and no upload improvement.  Oddly, downstream power level is now reading +1 (previously +7) at the modem info page (192.168.100.1).  The modem info page log tab shows a series of "No Ranging Response received" messages.  In the status tab of the modem info page it actually says the cable modem status is "offline" even though it is connected and loads web pages.  Also of note is that any access to the modem info page stalls for about 20 seconds (I remember the info popping right up in the past).  

Another speed test now shows 188/0.18 down/up speeds.

The cable service enters the house at the Cox box on the side of the house and goes up to the attic.  In the attic there is a new +15 db single output amp (added in March due to low signal levels) and after the amp are splitters feeding the internet, TV, and phone devices in the home.  

Ick. Amps and splitters. I find it best to have a two way splitter at the demarc, one going to the modem and one going to the amp and then from amp to TV boxes. Modems don't like amps I find. Can you post your signal levels. I want to see if you actually need the amp.

Over the years I have had amps and no amps.  Prior to March I had no amp for several years.  Cable enters attic and there is a two way splitter, one leg feeding cable modem and the other leg feeding other splitter for TVs, phone etc.  I was getting low cable modem signal (about -14 db) plus pixelization at TV and some poor phone audio so the present amp (+15) was put in before all the splits.  It is remote powered from an adapter in the house (many years ago I had an amp in the attic and the power brick died due to the heat).  Split layout is still the same... two way then another multi-way.

 I Can't figure out how to post screenshot of all the levels (insert image/video/file doesn't seem to work for me or I am doing it wrong.)  Downstream power is +1 for five channels and 0 for the other three.  S/N is 35 or 36 for all channels.  Upstream power is 40-43 across the four channels.