But this is not true!!! The worse you could do is to let the router to decide for you. And the best you can do is you to decide over the router... I've tested this so many times and smart-connection...

I think or i know why you getting such slow speed... bgn mixed mode... Try changing to only n or n/ac mode and you will see a huge diffrience in speed. Good luck and let us know how it went?.

I have Archer c7 and trust me but the one you have is far from perfect.

But they said that this router C5400 has very very good range in both 2.4 and 5Ghz ? Is it true that this is not correct ?

So what did you do that fixed so the speed in WIFI will always get full speed ?