Probably not. This isn't a simple problem at all, so don't exspect a simple answer.
As for game fuel, thats actually easier then you might think. Atleast in therory. Local IP is any individual computer in your house, and Local Port range is the ports you want open for that computer. Remote IP in this case is either your WoW server, or possible a broad range, depending on the need, and remote port is the port you want that incoming traffic to be routed to.
See, one thing alot of people mess up is not all forwarding has to be two way. Some traffic is one way. For example, when walking into a new city, the server just has to download some info onto your computer, you don't have to upload much info back. This is because your PC is doing most of the thinking, and the server is probably just doing time of day, enviroment, and so on. PvP is different though, thats a constant stream of data between players.
As for your modem, yea..umm, do you lease that? If so you might want to ask for a Motorola. I think TWC are phasing out the Ambits for the Motorola SB5101, you might want to ask them about it. Not that I think the issue is your modem mind you, but anything with a 1 page gateway (which I confirmed) is not ok in my book.