If your speed drops that much during peak hours, it can mean the node serving your neighborhood is overloaded (too many customers on the same node). We had the same problem years back and we kept calling for service calls until they finally fixed the problem (not sure if they added a node or replace a smaller node with a larger one). Also, where the cable come into your house, there could be a splitter device that has gone bad (it's metal and about the size of a matchbox). They do no stand up very well to the weather. Two years ago I was having speed problems. The tech replaced the splitter and everything has been good since.