Router not providing set DNS to clients

Have ATT DSL and recently have had trouble with internet access.  Thought it was the router failing at first so switched from an Asus RT-n16 to a Asus WL-520GU that I had on hand.  Was working sproradically so thought that fixed it but it failed after about a day.  I discovered it was a DNS problem.  If I set the DNS to google DNS IP on the PC it worked.  Seems that ATT (acturally an old SBC account) DNS is not working very well or maybe the routers are not handling it properly.   If I set the google DNS IP  in the router and have the PC get it automatically the PC gets the router IP but it does not work. 
 
Have been pulling out my hair on this one...  Need to check the router firmware and may either update or move to wrt/tomato/etc.  Any other ideas/suggestions?
 
 

Just found this:
 
http://www.asus.com/us/support/FAQ/1010145/
 
Need to update the software.

Good news Jim on the updated Asus firmware.
 
I was going to suggest giving PFSense a spin.
 
While the newer boxes do have more memory / CPU horsepower / more cache space than the older ones they are still doing much more work then they used to do.  The internet pipes are much larger than they used to be.  I still utilize DD-WRT on my older Linksys / Asus / Buffalo boxes (for mostly testing these days).
 
Here my newest modems have Gb network ports such that when I built the PFSense box put all Gb NICs on it.  It is understood that  you are utilizing DSL.
 
It is a very plug n play software totally managable via its GUI interface.  I have not been able to break it.
 
It is doing all sorts of things today.
 
You can install it on just about any PC these days. 
 
@Jim; maybe give PFSense a spin eh? 

Started to update the N16 router and it won't power up.  The lights flash on briefly and then nothing.  Found some info on bad capacitors. 
 
http://blog.jseaber.com/2014/09/21/fixing-asus-rt-n16-shuts-down-after-boot/
 
Two caps are slightly bulged - the one mentioned and one near the center of the board - so I will be replacing them.  There was a problem with DNS but the bad caps probably explain why the router would get flaky once in a while and require a reset.

Here is another reference relating to the Asus N16 router.  I am using OpenWRT today on a few test boxes.
 
OpenWRT Asus RT-N16