This is not your ordinary freezing/crashing problem.

When I first fire up New Vegas, the game runs fine. No problems. As the hours pass by, I'll notice the game will start getting much choppier and will being to freeze and crash very frequently.

This is not an overheating problem or a problem with Steam. All of my other games run fine. Anyone have any suggestions?

Mods can do that stuff.

This is not a mod problem. I've tried with all mods disabled. However, it could be a DLC problem. I didn't notice this until I downloaded HH/DM.

Then yeah that might be the problem the DLC.