AT&T U-Verse is a pretty decent service overall. However, their wireless access point (WAP) that connects to the main router is B/G and limited to 54mbps (in theory), but reality is only showing ~3mbps, even when sitting six feet away with no obstacles.
I have an older Linksys WRT400N router running DD-WRT that's simply connected as a hard-wired switch/WAP (b/g/n) and much faster and more stable than the WAP they provide us. I simply ran a CAT6 cable from the back of the main U-Verse box/router/gateway to one of the ports on the Linksys and turned off DHCP on the Linksys. That's it. When this is working typically, wifi speeds max out the 15mbps that we are subscribed at no matter where you are in the house.
I try to hard-wire everything if possible. However, whenever I would try to hard-wire their TV receiver, it would always crash the wifi on the Linksys. The TV receiver uses the IPTV protocol and is basically doing multi-casting, which is the root of the entire problem. So, long story short I set up the firewall on my Linksys (DD-WRT) to drop all the multicasting traffic on the atheros (wireless) interfaces.
If you login to DD-WRT, and go to Administration > Commands and put the following in the box:
ebtables -A FORWARD -o ath0 -p ipv4 --pkttype-type multicast --ip-source ! 192.168.1.0/255.255.255.0 -j DROP
ebtables -A FORWARD -o ath1 -p ipv4 --pkttype-type multicast --ip-source ! 192.168.1.0/255.255.255.0 -j DROP
Click Save Startup, reboot the Linksys, and you're done.
Other examples on the internet, show similar solutions using eth1 or eth0 in the last two lines as well as other options like "-A OUTPUT", and it doesn't hurt to include them, but, the only thing that was definitively required for my setup to work like initially, is what's above. I think the --ip-source and -p switches may not be required as well, but again, it doesn't hurt much.
Life is good again, even though I don't have many wi-fi devices hooked up at any given moment. Hopefully this saves someone a lot of the frustration I dealt with for days in solving this.