What do the modem's signal stats look like ? Try getting them here http://192.168.100.1 or here http://10.0.0.1
Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.
Your signal stats are o-k / in spec. With numbers like that I would have to assume that their signals stats are o-k as well. This is not to say that a capacity / congestion issue may be causing your lag.