I have 600mbs internet.  The network was suddenly very slow.  I tried resetting everything, no change.  I connected my pc via ethernet cable direct to isp modem.  600 up and down.  Connected modem back to deco main, 100 download, 600 upload, I have cat6 cable between isp modem and deco, I have cat 6 cable between deco and gigabit switch.  My pc is connected via cat6.   I tried  bypassing the deco, and connected the isp modem to my switch, speed tests were good 600/600.  I replaced the main deco with another one, still only getting 100 download, I have tried hardwired to deco and wifi, it just will not allow download over 100.  When I first set it up, I got the same speed hardwired as I did on wifi through out the house.  I went through and set speed 1000 in qos and made sure no scenes or clients were on.  No port forwarding, under nat sip alg and upnp are off.  No change.  I don't know what else to do.  I have 5 decos and I guess since main is slow, they are all slow.  There was a firmware update that went through, now I can't get anywhere near my isp provided internet speed and doing anything online is laggy and slow HELP, what else can I try?