CM1000v2 extremely slow upload speeds

I'm sure there is a splitter in the attic. Tested direct to modem and still at 6mbps. The thing I don't get is that it was getting 100-200, same cabling, same splitter, etc with the XB8 gateway. Got a tech coming out today, and there's some known issues in the area with some OFDMA channels with my neighbors, but the last tech out confirmed they were good on my line (he swapped me to a new port at their service). I will have him test the line going into the modem as well, as they only did it at the street/port last time. Just interesting to me to get different results out of different modems with this much difference. (of course I would expect it to be somewhat slower, but going from even 30-50 to 6 is pretty significant).