Right now I'm dusting off an old Linksys so it can handle the house while I mess around with the firmware on the main router.
It does appear that there's a bug in the way the older dd-wrt firmware handled DHCP renewals... I think I've fixed it with a correct command? Hopefully the upgrade and reset will continue to fix. I'm actually not running any particularly fancy features. Like I say, it's not a speed issue... it's plenty fast between these hiccups.