I have some of my gears on Slushpool havn't seen a problem in a long time, you could try the pools Bitmaxz suggested, currently I use Slushpool , Viabtc and Cksolo , non of them is having a bad time, the stale shares however can very well be a connection problem.

 i don't know about your networking background but you should monitor the packets going to and out of the miners , cables , latency and etc.. but all of this is not needed unless all the other pools mentioned here give you the same issue.

Also always use a pool server closest to your location, you can ping the server using CMD with ping -t and let it run for 15 mins see if you get any packed loss or not.