Whats the highest speed DL package you are paying for from your ISP. I'm buying a 10Mb connection with 1Mb up.
Have you set up a static IP address for the xbox in the router?
Your Gamefuel rule is correct, however lets remove the check mark for Dynamic Fragmentation and disable the Gaming rule as that option is not needed for game consoles.
You can also change the Local and Remote port TO Ranges to 3074 and give that a try.
If this doesn't help, I would like you to do a full factory reset on the router. After it resets, don't change anything, just connect up the xbox and get online and see if you see any improvement or not. If you do then we need to help you configure the router. Sounds like something is quite right here. I presume that connecting directly to the cable modem you get good speeds and connections?