Lately I've been getting wildly fluctuating QAM values on my upstream. Rapidly dropping from 64QAM to 32QAM and 16QAM across the board. I believe it is causing random drop out but I don't seem to have any impacted speeds or at least its very minor that I haven't noticed it.
I've had a live broadband graph running for the last month. You can look back and see if there is a trend.