Default Slimkat Network Connection problem

First, Hi. I have a Galaxy S3 International Model, I live in Central America (Panama to be precise) and I installed the ROM Slimkat. Is very smooth and fast and simple which I like but my network conection comes and go. Is like it comes but immediately it goes. So i don't have Data nor signal to make calls/SMS.

And the most strange thing is that I have the IMEI in the phone, just that my network connection leave and come. But comes for only 5 sec, so it is always with no network status. I made an EFS backup and restore it but no results.

I would be really greatful if someone can give me an answer.