I think it's normal to see one or two Dynamic Range Violation errors when you first reset the modem and it's figuring out the right upstream power levels. For a while I was getting 10 or more of these per day, and Cox sent out a tech to replace a bad exterior cable and bad amplifier on the pole. After that I didn't get any of those errors for a week, but as of today I'm getting 4 or 5 per hour. Based on the meaning of the error I don't think it's normal, but I only seem to get a momentary upstream glitch when it happens so maybe it's not a high priority to fix.
The T3 and T4 timeouts can be more of a problem. I've had those before and they always caused major downtime. As you probably know, anything you see in the cable modem status or event logs can't be caused by your computer, router, or Ethernet cable. Errors in the log are caused by your modem, interior coax cable, exterior cable, or Cox network equipment. If you've checked your modem and interior coax cable you probably need one of the forum moderators to look at your account.