What is the model number of the WTS transmitters, how many do you have and where are they attached? If they are Arris/ Motorola VAPxxxx, then the connection to the modem is Ethernet, but the transmission is 5 GHz Wi-Fi to the other transmitter(s).
Is the modem located in a basement in a difficult area for Wi-Fi - near furnace and heating ducts? Where is the PVR in relation to the modem? Would it be possible to move the PVR to a TV that is closer to the modem?