Xperia Firmware update problems c6606

Hi, Guys. I recently flashed a new Rom on my T-mobile Xperia Z. However whenever I update to 5.0.2 Lillopop I cannot get cell reception. I live in Guyana so I bought the phone online and had it shipped and unlocked. I have tried both the c66103 and the c6616 however in both , as soon as I update to Lollipop I lose cell reception. All other updates up to Kit Kat 4.4.4 work perfectly. Any advice? I figure it must be something like a baseband problem. I have already tried flashing that however the baseband # does not change. Any advice would be helpful.
Best Regards