Baffling MBP internet connectivity issues

Hi everyone, apologies for the long text but I want to be thorough. I've tried everything and nothing will work.

A couple days ago I found that my 2009 MacBook Pro (running 10.8.5) was loading pages very slowly, and sometimes not at all. I experienced the same before on both Safari and Chrome. I should note that throughout this whole ordeal my iPad Air and iPhone 5 have functioned on my network perfectly, as have my roommate's old MacBook Pro (non-unibody) and 2011 MacBook Pro. Just to be thorough, I tried resetting my router, restarting my computer (duh), etc. It's definitely having something to do with my computer, not my router or home network.

I tried sending some pings in Network Utility. When sending to google.com I experienced anywhere from 80-100% packet loss.

I tried deleting /Library/Preferences/SystemConfiguration/ as some people on here have suggested. No help.

Today I went to the Apple Store. While waiting for my Genius Bar appointment, I grabbed a coffee and checked with the wifi there at the coffee shop. My phone was able to join and my labtop wasn't. But, my MBP was able to join the Apple Store network without issue. Weird!

The Genius did an extensive test and made sure that all my hardware is fine. All cleared. At this point, the only possible issue is on the software side.

I got home and downloaded a few udpates (using my ethernet cable...it works fine) that didn't have anything to do with networking (iTunes was one of them) but I just wanted to be sure. Nothing helped. Still, my pages were loading extraordinarily slow (taking about a minute, if they even loaded at all).

I then tried clearing the DNS cache, as explained here: http://support.apple.com/kb/HT5343?viewlocale=en_US&locale=en_US

I thought I had fixed it. Everything was working fine, and then 5 minutes later the problem mysteriously reappeared.

Now, I'm not even able to connect to my home network (I get a "timeout" error message when I try). Yes, I've since restarted, once again, just to make sure.

I've even tried creating a new User on my MBP, and creating a new Location in my Network Preferences. Nothing.

Lastly, I should note that I use Microsoft Remote Desktop to connect to a slave PC running Windows 7. When my Mac's wifi is on, I'm unable to connect to the PC. When it's off, I can. I use an ethernet to connect the two (long story short, I send MIDI messages to the PC and recieve audio back, hence the need for ethernet).

Anyone have any idea what's going on here? I feel like I've exhausted all the possibilities, or at least the ones within my realm of knowledge.