The engine hiccups or infrequently quits at highway speed then restarts easily. The dash coolant temperature gauge goes from normal reading to cold reading then bounces back to normal intermittently. Setting multiple codes PO118 ECT high input, PO299 EP Turbo/charger underboost, P1378 INJ Module FICM supply voltage low, VO155 lost commun with TCM, UO105 lost commun with FICM, UO100 lost commun with ECM/PCM, and PO606 Internal PCM fault. Replaced the PCM which didn't fix it. Where should this dummy look?

 

I would start by following wire harnesses under the hood and make sure everything is plugged in TIGHT. Sounds like a loose connection to me. Check where the wires go into the FICM, it's on the drivers side valve cover. Take the coolant bottle off and push it out of the way, you'll see the FICM.

 

You sure your battery voltage is good?