Using GER device on FR network (n9005)

Hello ,

Since two years, I live hell with my GSM bought new, but normally intended for the German market.
I tried several operators / sim card but nothing works. Today using lollipop (OTA ) my device is slow, laggy, bugged... and I 'm sick of losing the networks again and again ... so i think i need new software for my device.

Right now I'm rooting the device and then i will need a good rom ..... but which on (?) ( I DL this rom " N9005XXUGPOF3_AryaMod_V7.3_Public " because....I don't know .... it must be correct , right ?)

Then I wonder: Do my network problemes are comming from the fact it's a device for german network....is there anything to do for the modem, maybe it's possible to force it as if it were a device intended for the french network... ?

Here Many questions .... I love this phone , it saddens me to change because of possible software concern... : /

Thank you for your help and for your indulgence for the noob I am.

Best regards

Modele : SM-N9005
Version Android 5.0
Version de la bande de base : N9005XXUGBOD3
Kernel 3.4.0-4540543 dpi@SWDD6216#1
Numero de version LRX21V.N9005XXUGBOE9