v5 is very very old and no longer supported.
Try v7 (free upgrade as always).
There is no way that JMR should be caching 2GB of data in memory. Something else is going on if you are seeing JMR using 2GB of memory. Memory management is handled by the core .NET subsystem (part of the OS now).
If you are still experiencing this with v7 then please give an example of a url hosting a video where this is occurring and a screenshot showing 2GB of memory usage by the jmrp.exe process. We can then go from there.
I've noticed that whenever I use Jaksta Media Recorder (Version 5) to grab/record rtmp-based streams, the program tends to slow down completely when there are streams with a very high bitrate. The private bytes in Windows dramatically increases, and I can only use the program again if I force it to close and restart. Apparently this happens because it can only address 2GB of memory, as a 32-bit application, and because it tries get more memory than what's allowed, the program freezes up. Is there any plan at some point to make this a 64-bit application, so Jaksta is able to use more memory and eliminate these freezing problems???