|So, your Motorola Surfboard had NAT that you turned off? Whats the model number of the modem that they gave you?|
This all started when you go the new cable modem right? And your digital cable box is lagging too. So it's something with the line if you are having problems with both.
How far are you from the road?
I had this problem too, because my house was too far from the drop. They had to put in a 3/4" thick coax to solve the problem. There was just too much noise and resistance in the old cable.
Keep calling your cable company and tell them to replace the entire line.