Upgraded Premier to Ultimate, SB6141 to SB6183. Speed went down!

I recently upgraded to Ultimate (300down), and got a refurbished SB6183 16x4 modem to be able to get the speeds up. I was getting about 80down on Premier before the switch on my SB6141, but when I installed and activated the SB6183, I was only getting about 30down! I called and talked to tech support, and they didn't know what the issue was. I decided to return that modem and got a new 6183 instead in case the refurb was bad. Installed/activated it today, and got a Cat 6 cable to go to my router (E1200), and I'm still only getting about 40-50 down, sometimes as low as 25.  Upload seems fine, from 25-35.

It looks like I'm bonding to 16 channels down, which is good. I'm at a loss.

A tech on the phone said it could take a few days for it to get up to speed, but it still seems wrong. 

I tried hardwiring to a laptop, and only got a marginal bump in speed.

Was going to set up a technician appointment, but they said it could be $75 -- but said they won't know till the tech comes, because it's the tech who decides if it's my fault or not, basically. Ugh.

Any ideas?

Image uploader was being weird, so modem stuff here:

http://imgur.com/a/jFWxG