Stop Background Apps from Closing

[CarterGuy]

So I'm rooted and running the stock 2.2.1 update and now it seems when I open more than two apps, it closes one in the background. It gotten really annoying that when I'm playing music and browsing the internet and I get a text, when I switch over to the text either the music stops playing or the browser closes. Is there any way to stop the apps from closing. If I need to flash a custom ROM I will. Any help would be much appreciated.