Why is my internet still lagging with a new router?

I recently upgraded from an old router purchased at WalMart (I think it was Cisco but I don t remember, my fiancé handles that stuff) to a new Linksys AC1200+ dual band router. With the old router, I wasn t getting very good signal at the far end of the house and it got worse as the router got older, and we had problems with slow loading when streaming movies. The new router is 2.4 and 5ghz, I was under the impression it would have better range too but it doesn t seem to be any better. For some reason when I connect on my phone to the 5ghz wifi, it just changes me back to the 2.4ghz. My phone internet is running at about the same speed as before and while streaming we now lag very badly and the Internet stops working altogether for a minute, then comes back on, then goes out again. I don t understand what is going on, do you think I might need a new modem as well?

P.S. I pay for the premium (100mbps download, 10mbps upload) Internet with Cox. When I tested the speed yesterday with the new router it showed us running 30mbps download and 4 mbps upload). We have two smartphones, a tablet, two blurays (one wired and one wireless, but we only use them when wired in), a laptop, desktop, and two kindles we connect every blue moon to download a book. Around a couple weeks before upgrading the router, we also upgraded the Internet, so considering we had a cheap router and slower Internet before with the same amount of activity, should our internet be lightning fast now?

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