First off I would HIGHLY recommend you get wireless router to put behind the 3801 Gateway. I use a Linksys router with a Tomato-Toastman based firmware. This basically let's you bypass a lot of the traffic shaping the 3801 gateway attempts to do but fails severely in many ways.
1. For my VoIP/Skype/gaming I put the router into DMZplus mode which gives it the public IP, open up all traffic to the router/disable the 3801 firewall for the device, and then I go an extra step and go into the firewall settings of the 3801 gateway
and UNCHECK(to disable the 3801 from touching anything):
Stealth Mode
Block Ping
Strict UDP Session Control
Excessive Session Detection
TCP/UDP Port Scan
Invalid Source/Destination IP address
Packet Flood (SYN/UDP/ICMP/Other)
Invalid TCP Flag Attacks (NULL/XMAS/Other)
Invalid ICMP Detection
Miscellaneous
and CHECK(to allow all inbound):
HTTP
HTTPS
FTP
Telnet
SMTP
DNS
NetBIOS
POP3
IMAP
NNTP
IRC
H323
All Other Protocols
I know this is kind of not needed since I disabled the firewall for the gateway but it seems to speed things up a bit in my opinion since it's not actively looking for attacks or not allowing certain traffic through.
2. Then in my Tomato firmware I changed my dns servers and un-checked the option in the firmware for : "Use received DNS with user-entered DNS"
This let's you bypass the 3801's dns which is slow and unresponsive at times I have found. So this dramatically speeds up everything.
3. Specifically for Youtube I block these IP ranges from the post I made here:
previous postAll this let's me have a smooth experience with U-verse, and I should mention I am on the 12mbit/1.5mbit internet tier. No tech is going to be able to recommend you do any of this, and it may not be for everyone if you have devices other than your STB's/Wireless Router connected directly to your 3801 gateway(as this would open up those devices to attacks). With that said everything except your STB's should be connected behind your router...not directly to your 3801 gateway if you go this route.