Couple of questions about poor performance - Time Warner Internet

This question is about "Couple of questions about poor performance", with Time Warner Cable internet and apps. I'm in NW Ohio the Dayton area and have the TG1672G modem/router with the 50mbps package. I've had it for 3 months now and average 5-12mbps. After some reading I change some settings in the modem and got 49.88mbps. I moved the modem to another room and it went back to normal. Moved it back and still normal or below. There's a few different splitters here, a -3.5db and a -5.5db. Which do I use with the modem? And there's a power inserter in the other room where I'd like to keep the modem, without the A/C converter plugged in there's 0 connectivity. Should I have the modem wired from the inserter?

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