Slower Internet Speeds

Hello, I have verizon gigabit internet. Since February I built a pc and was enjoying 700 mbps speeds using ethernet connection to my Nighthawk XR500. For the last couple months, I have been experience under 50 mbps speed and cannot figure out why. I have tried updating drivers and software and firmware but nothing has worked. I purchased boostspeed and optimized but has not worked. Any help would be appreciated. I get speeds of around 500 to 600 on my phone.