Lucas,
I haven't used Vista, so I am only guessing here.
- Regarding your hang problem. As you are using RadarBox without an internet connection, you could try deselecting "Share data", "Download photos" and "Process Network Data".
- My sensitivity is the same or better since the Firmware upgrade and V1.3, but look at the Timeout settings for Live data. Try experimenting with these settings. There are also separate settings for Network data, but as you are not using an internet connection, these will not make any difference. I notice that all the aircraft over Sardinia on your screen shot are grey in colour, which mean they are all timed out so you are probably only getting occasional hits there. Changes to the timeout settings when V1.3 was installed might account for this.
Also, remember that sometimes there is less traffic, especially at night.