Wireless Adapter Problems

Okay, so I built my new rig back in November and had originally used an old wireless G adapter for the first couple months, but decided to upgrade to a wireless N adapter in January since I had a wireless N router in my college house. I bought the Asus PCE-N15 wireless N adapter the is supposed to go up to 300mb/s. When I lived there I used the Windows drivers with no problems and got about 10-15mb/s download speed, which didn't seem bad since I was in the attic bedroom and the router was on the first floor, 2 floors down, and it was a crappy Belkin wireless N router and one of the first one from years ago. Once I graduated I moved back home to save money, and my parents have FiOS, which provides/forces the Actiontec wireless G router/modem, as our package is I think the 25/25 package/speed. Ever since moving home my network connection has been very unstable as the bars will go from full, down to two, then three, then full, etc. It will also disconnect, which is awful when I am gaming. My speeds are down to about 5-9 mb/s down, sometimes lower, but the upload remains at about 10mb/s. I am in my basement, one floor below the router and not very far. I do not think it is interference as I tested my MacBook, sitting it on the floor right next to my PC, and speedtest ran about 29mb/s down and 23mb/s up. I am baffled as I even checked with an app for interference which didn't come up with much, and I changed the channel to help with that as well. I am using Windows 7 64bit as well, not sure about the networking compatibility issues with it.

Do you guys think this has to do with a crappy adapter? Maybe problems using a wireless N adapter with a wireless G router? I'm getting really pissed as I cannot really game online much right now because of the slowdowns and d/c's. When I test my ping is about 35ms which is good, but when I experience slowdowns my ping for BF3 servers, browsing the list, will be 90+. Any thoughts or recommendations?

Thanks. Also, I have the power saving setting disabled as that was my original guess.

Asus PCE-N15

EDIT: I am also running Avast! Free Antivirus. Once I'm home from work I may try disabling it and reinstalling the drivers to see if that is the problem, or disabling in general to see if either of those work as a solution.