My New "Upgraded" router fails with Wi-Fi. Help Please!?

[BballBoyNtn]

I have owned the same Linksys WRT120 router for 3 years now, with no problem. It worked fine until the number of gadgets in our household started growing, and it started to become dated. I went out today, and got the Linksys EA600, because Linksys was great so far, and since I'm always on media, I really wanted the dual band capability for the 5ghz band. So I set up the router as instructed, and my desktop worked fine, because it was direct connect, but anything wireless failed with Wi-Fi. My Issue isn't as simple as "My devices won't connect". My devices connected fine, but my connection was inconsistent. I would get on my youtube app on 2 different devices (IPhone & Galaxy Tablet), and it would load long enough to play one video, then it would fail to load anything else. My App Store fails to function, and loading pictures on sites, like facebook, failed past that point. The strange thing is, it'll let me stream video on the TwitchTV app just fine. I'm so lost on what to do. After being on the computer and phone with customer service, I'm lost. They lead me to a dead end, then tried to feed me BS, saying it was my tablet, after I told them that it was happening with different devices by different brands. I just need a solution, and anyone willing to help me solve this will save me the trouble of returning this device. Thank you.

[hbk]

>try reducing MTU size to 1350 or 1400 if u haven't done already