" Usage on website is completely wrong. Says I've used 165 mb in a week yet history shows 6gb in one day."
New accounts have their usage reset daily for the first 10 (HN9000) or 20 days (HT1100).
This would account for "usage" showing only 165 MB but "history" showing a different value.
The 6 GB in one day is a considerable amount of data for a capped service and is indicative of a lot of activity that you may not be aware of. A high amount of background activity would surely have a negative effect on your speeds.
"Sometimes it just disconnects."
Can you be more descriptive here? A screenshot perhaps?
When this nest occurs can you open the modems SCC at 192.168.0.1 and note any error or condition codes and post them for us? (remove your SAN in any screenshots!)
"Sometimes my screen goes black"
Frankly this sounds more like a computer/hardware/video card/video driver issue than the result of a loss of Internet connectivity.
Once again speed tests must be performed from a computer connected directly to the modem. There simply are too many potential router induced influences that can affect your performance while trying to establish baseline performance levels.
The 6 GB in one day is a considerable amount of data for a capped service and is indicative of a lot of activity that you may not be aware of. A high amount of background activity would surely have a negative effect on your speeds.