Since cable connections are shared with your neighbors, and as you say you live in a high rise, you're in all likelyhood running into cable congestion. You could try setting your router to another channel or plugging your computer into a wired connections, although it's likely just cable congestion.
I have the comcast performance internet and have noticed extremely slow wireless speeds (even when I am right next to the router). These slow speeds seem to often be during peak times (5pm-9pm). I live in a high rise apartment so I am wondering if there is some sort of congestion when everyone is on it at the same time. What's odd is that when wired, I still have good speeds. Here are my specs:
Wired speed: 25mbps
Wireless download: 1mbps
Wireless upload: 4mbps
Windows wireless connectivity : 144mpbs with excellent signal
Router: Linksys E3200 Dual-Band N
Modem: D-Link DCM202 (docsis 2.0)
I am wondering if maybe I should update my modem to the recommended DOCSIS 3.0 but I am not sure if that would help?