I don't know if this will be usable for your case, here at home the aDSL modem tries to be the resolver. The trouble is with the ISP: their DNS servers are quite frequently unreliable and unstable. They even affect the PPP connection sate, as the modem firmware uses that to trigger self induced reboots, while link is present and working. You can imagine how frustrating this can be for users not realising what's going on in fact.
To solve this, multiple times with various different locations, I ended up setting up local resolving DNS server, recently this became Unbound, on the gateway OpenBSD system, and it does resolution directly querying root DNS servers. I think this solved it for me ultimately many times. For this ISP, this is the solution here, I believe this can help others.
