Slow Internet Speeds

We have been with Cox for approx. 1 year. We had Century link before them. I have a 300meg connection with Cox and had a 40 Meg with Century link. With Century link I had no problems with Facebook or any other websites slowing down. With cox it seems like every site is slow to load and pauses when playing videos. It has been like this from the beginning. I test my speeds with the cox speed test and they always show around 300megs. Facebook is always timing out. I have used multiple browsers, and PC's. I am directly connected to the modem. I have not contacted cox about this yet. I wanted to see if you all had any suggestions first.