The /3GB switch is not in the boot.ini file. It's also not in the other server that is using 3GB of memory.

I did a little more digging and found that AWE is enabled on the server that is using 3GB of memory, and not enabled on the one using only 1.6GB. I'm fairly new to this environment so not sure why it's on for one and not the other. Would that make a difference? I thought AWE was used only if there's 4GB or more of physical memory.