Weak GSM Network after Screen/Digitizer Replacement?

Ever since I replaced my screen on my Verizon 32GB 4s, my GSM Network service has been very weak. It will fluctuate from 1 bar to full bars and 3G, back to roaming over the course of a few minutes while driving. I have sent the phone to 3 iphone repair shops that have been unable to resolve the issue.

We have changed out all the antennae parts and also ensured that the little blue inductor above the main antennae connection on the logic board is still present(not sure if working). Wifi works great. 1 shop did switch out the logic board with another phone temporarily to see if that resolved the issue and it did.

Any suggestions on how to troubleshoot the issue on the logic board to see if this issue can be resolved without replacing the whole board?