SB6183 slow speed

Hi Guys,

I have SB6183 and it works fine for few minutes but after no more than 18 hours, the speed drops from 100Mb to 3Mb and very high delay in ping,

if I reboot the modem everything work again temporary

I replaced the modem and the problem still there,

ISP was useless to troubleshoot, if i change the modem with different model it works fine.

any idea of how you can troubleshoot this issue?

can I login into the serial port and get some diagnostics?

please help.

thanks