I followed these videos to fix my Nexus 5 (the earliest batch 310K), GPS:

At a window of my home (surrounded by tall buildings), my GPS lock time decreased from 90 seconds to 25 seconds using GPS Status & Toolbox app.  UPDATE: Unfortunately retesting this the next day the results are not consistently good.

Extra care is needed to make sure the central NFC and Wireless charging contacts are closed when closing the case, otherwise these functions will fail.  I find it best to close the central clip before closing the sides when reassembling the unit.

Now my Nexus 5 case cannot close perfectly at the GPS antenna corner.   I need to use a hard case to hold it together.