Motorolla SB6141 Modem

I switched from Residential to Buisness I have a router and seperate modem, not the combo thing.  I bought my own modem which is the Motorolla SB6141.

When looking at my modem settings its saying the DHCP Server is enabled. Wont this give me issues as my router is dishing out ip addresses for my devices?

Been doing a little googling and I read, dont know if it is correct but the modem should be in bridge mode ?

Reason Im asking is I never had issues with my NAT being strict when I was on residential, as soon as I moved to buisness im having issues with a strict NAT. I done what I can router side, and I can get by by using port forward but after a few days it goes back to strict and I have to reboot he modem to get my NAT back open.   I keep reading about double NAT and that my modem shouldnt have DHCP enabled as my router is doing that job.

Im no network guru so Im trying to find out why Im having this issue.

thanks