Your downstream power level is fine. Some suggest to make sure it's between -6 yo +6. Some say -8 to +8.

Cable Modem standards (DOCSIS) says anything between -15 to +15 will work. When you get nearer either end though you would see more issues than if you were in the middle. You are well over half way towards the middle. Plus your downstream SNR is well above 30db.

Upstream is well within limits as well. 55db or less is what to aim for. This is kind of a way to show how much work your modem has to do to get a good signal transmitted. Lower is better. But 51db is just fine.

Here's a quick compare:
You: 36db
Me: 35db
You: -7dBmV
Me: -1dBmV
You: 51dBmV
Me: 50dBmV

So unless the connection is just dropping completely, your signal levels are fine.

You can setup a monitor on www.dslreports.com and have them ping you every 5 mins to monitor your connection. At least that way you can tell if it's your connection or your computer.