T3 time outs mean the cmts (big computer up the line that manages cable internet) has not recieved a response in the time it expected. This is usually because you have a upstream/return impairment in the coax system. Most of the time it's going to be local but it can be a system issue. Locally you may have too many splitter running the return/transmit strength up beyond the maximum so that the cmts is receiving a weak signal, or noise/interferance is on the line and the data cannot be understood and thus a request or multiple requests to resend the data are required.
Can you post the levels?