Nighthawk X6S AC3600 Router R7960P wired speed issue

I have a Nighthawk R7960, CM1100 modem, and gigabit internet with Xfinity.  We have a computer using an Ethernet connection to the router.  When we first got the gigabit internet service, we were only getting around 300 Mbps over the wired connection.  When we moved the wired connection directly to the modem, we got 950+ Mbps, so the problem is not with the internet service.  Xfinity technical support suggested doing a factory reset on the router.  After the factory reset of the router, we got 950+ Mbps over the wired connection to the router.  Since then, we have found the speed over the wired connection drop down to around 300 Mbps three or four times.  Reseting the modem and/or router doesn't fix this speed issue.  I have found that only performing the factory reset on the router will fix the problem but the reduced speed issue is still a a recurring problem.  The firmware is up to date.  I have seen similar posts suggesting the factory reset.  Is there a better, more permanent solution to this speed issue with the router?  If I can't find a better solution, I'm going to switch to a different router.