First, this is "Community", not "Support", OK?
Sounds like you are running 32bit Windows and/or 32bit QlikView. A single 32bit process, e.g. QlikView, can only address a maximum of 2GB (or as you have found with the /3GB switch, 3GB) in a 32bit environment.
You need to run Windows 64bit and QlikView 64bit to get the full memory. There is no licensing difference for QlikView 64bit, but there is for Windows.