Odd issue between 32-bit and 64-bit versions

I have a very old system with Windows 7 and 8GB of RAM, but every time I load up the Campaign in 64-bit mode, without fail, the game crashes once I reach Pac at the safe house; strangely enough when playing campaign in 32-bit mode, the game hardly ever locks up at all.

I've installed Dot Net Framework 4.5 and installed both versions of vcredist, but the issue persists.  My question is, shouldn't the game be running MORE smoothly (thus less likely to crash) with full access to the RAM...?

I am also having trouble loading multiplayer on any server.