Love to see threads like this
For the data/cell, move over the libril* file(s) in /system/lib from our Verizon stock ROM to the GPE ROM (do one at a time) and see if that fixes the issue with data. Also may want to verify the build.prop references the appropriate RIL ffilename if different from in GPE build.prop.
For SMS/MMS, try moving the *apns* files from /system/etc on our Verizon stock rom to GPE and again see if that fixes the SMS/MMS issue. If that doesn't resolve it, it's probably buried in the framework-res.apk under /xml/. You could try extracting the contents of the Verizon framework-res.apk and simply copy over the /xml/apns.xml into the GPE framework-res.apk.
Biggest advice I can give you is only move and test 1 file at a time. Sounds Tedious but it will save you sooo much time in the long run.
Good to see you working on this