Re: [HSI] So I had a Motorola SB6121 provisioned (slow)
Your numbers look similar to my 6121's so I can't really help, but what firmware do you have? Mine is Firmware Name: SB_KOMODO-188.8.131.52-SCM00-NOSH and has worked fine.
I will say I still have that 1970 date error in the modem log, which hasn't corrected for me. They told me not to worry about it, someone hadn't changed a date in their equipment... it wasn't my modem.
Hope you find out what the problem is. I had to replace my reliable Linksys router to get the higher speeds after getting this modem.