So I'm at 48% percent completion. Whenever I go to load the game, it freezes in the loading screen. I thought this was strange, considering the game was fresh out of the case (360 version). I took the disc out to look and there were no scratches. Its not just the game that freezes, its my entire xbox. I can't load the guide or anything.

When I tried loading my saved game for the 100th time, not only did it load, it gave me 6 achievements (worth 125 points) also. I never actually earned these achievements and some of them would have been impossible to earn at that point in the game. The achievements are as follows:

Partners in Crime - This requires you to play co-op (something I hadn't done yet)
Hail and Kill - Destroy 50 items using melee attacks (again hadn't done that yet)
Be Quick or Be Dead - Snipe 50 enemy vehicle drivers (I haven't sniped 1 enemy driver)
Billion Dollar Babies - Earn 1 billion dollars (I have 4 million)
Longing For Fire - Max mood with Chinese (I haven't encountered the Chinese yet)
Eat the Heat - Do a burnout (again havn't done this)

After getting the six achievements, it let me play the game. The next time I tried to load it, it would not work. Has anyone else had this issue? Or is it just me?

So it loaded again and I got 3 more achievements. Again, these achievements were for things I couldn't do yet. Whats going on?

I think you should post at Pandemic Forums they may have explanation for what happened to you.

Captain Crunch I didn't get anything frozen at all but got those six achievements for doing nothing.  I just talked to the girl and when I exited I got all of those.  I haven't done any of those either but I am happy ;)

I'd try some memory maintenance on your xbox.
Try this it will not erase any or your game saves: