graysky
dont want to hijack this thread but i feel its similar, your setup closely resembles whats describe in #2 at this link How do I configure my devices to use Pi-hole as their DNS server?
Reading the instructions from this page got me up and running quickly but...
The last thing they mention is to go into pi-hole dns settings and set the only upstream DNS IP pointing back to the router. they did not really explain why, but I would have thought this would cause a loopback issue with the router forwarding DNS to pihole and then pihole sending it back to the router bank and forth?
I am also using ddwrt and got it up and running but the new dnsmasq support 4.0 has introduced has me excited about getting getting more detailed reports from individual clients rather then them all look like they're coming from the router itself.