MacBook :: Download Speed Decreased With Airport

It started 2 months ago, ever since I got my machine back from the top case being replaced. I've had some Airport problems, the first thing is distance. I used to be able to go all over the place in the house and it worked. It says I have a full signal strength, but it's it and miss on it working from my living room (which is really only 3 rooms away with not very thick walls). I used to be able to sit in the living room and work on my computer for hours, but like I said it's it and miss on the connection. One minute it's working the next it's not.

Another room that seems to be the bedroom, which basically 2 rooms away but can see the router down the hall thing. The bedroom door opens to those two rooms. Here it works, but I sometimes have to wait up to 3 or 4 minutes the web page to come up. Safari 5.02 is the worse compared to Fire Fox.

My download speeds have decreased as well, my top download speed is 160k/sec but lately it's been 140k-120k/sec.

Now that I have giving you too much information, do you think it might be the MacBook or the Router. When they where putting the new top case on it could they moved the Airport antenna somehow. OR should I reinstall Mac OS X thinking that might fix the problem.