Wi-Fi issues 70Mbps Download Dropped!!?

So I recently had Extreme 105 internet installed at my house, (I work from home connecting to many computers) and the download speeds are supposed to be at 105Mbps and 12 upload. So a Comcast tech came out here on Sunday and installed it with a SMC modem with a wireless router built in. I was getting 110 d/s and 13 u/s wired, and wireless at 70 d/s and 12 u/s. Two days later me and my wife were getting bad signals not too bad just 3 bars, but with the same speeds. A Comcast tech came back out here on Tuesday and installed a modem without a router. So I went out and bought a router and it only downloaded at wifi 15Mbs and upload 12Mbps, so I went back and bought another router and it did the same. So then I went out and bought a new DOCSIS 3.0 Gateway, had the best reviews and its doing the same!? But the whole time throughout this process I am hitting 105 d/s and 13 u/s through wired. This is also done testing on four different laptops, all only hooked up once WiFi and sitting next to router. Comcast wont help me with this since this is a WiFi issue. I have tried checking channels for better channels, as well as its in WPA2 mode AES.