High # of Uncorrected Errors and Issues with Upload Speeds

I have been using an MB8611 for 2 years with no issues. Downloads at 1.4G, uploads at 40Mbps. A week or so back the modem started showing high numbers of uncorrected errors, upstream power levels of >50 dBmV on each channel, and then started rebooting itself. Several times per hour. 

I checked the connections, and put a new 2-way Antronix splitter in front of it to rule out the 6-way Antronix amplified until I had - no change. I had a tech come out. 

He tested the cable where the modem is and said it was all good - the numbers the modem is reporting meant nothing to him he said. So he went out and switched the outside box and connectors for new, and said that was all he could do. The effect was the upstream power readings dropped to ~47, and he left. The uncorrectable errors continued. As did the random modem reboots. 

I switched back in my older MB8600 to see what effect that had - and while the reboots have stopped, the uncorrected errors have not, and now my upload speeds are stuck at ~6Mbps (downloads are back to <1Gb for now as expected but in the 900's, which is fine)

So I think I still have an issues with the uncorrected errors, and this upload speed isn't right. Any suggestions? 

I don't seem to be able to post a screenshot, so here's the first few lines of downstream. The % rates of corrected/uncorrected are similar up and down. The modem has been up for 22h.