I had a similar annoyance with resolution. The XFCE manager seemed convinced my card was only capable of 1024X768 @51hz for some reason. My personal experience didn't involve EnvyNG, as I'd found that the newest nVidia drivers didn't work whereas the previous one did. Can't remember the version number off the top of my head though.
As far as automatically adjusting I don't know of any programs that will, but if you go into a terminal and type "nvidia-settings" it should come up with a menu that will let you adjust the resolution using nVidia's settings instead of XFCE's (if it complains about "missing authorization" or something when you try to apply the changes, go back to the terminal and type "sudo nvidia-settings", just make sure you have all the settings right since you have administration rights in sudo mode).