Yeah, thank you very very much !^^
I used the "PG59IMG Doubleshot TMOUS 1.28.531.9 - Radio 10.48.9007.00 - 10.12.9007 signed.zip", flashed it through Fastboot and now it seems that my reboots are gone, reception is just fine and everything works like it should.
I´m very happy now
Will test it a few Days and then report back.
@ Fuzi0719: In the Threads i´ve read they sayd, that with some Roms the integrated Kernel causes this Problem with the newest Radio and in Standby the Modem restarts, which causes the Reboot.
Thanks again and best regards