I have a 2016 F-150 3.5L V6 Ecoboost truck. Drives fine for first 20 minutes, then a 'thump' happens, which seems to be a shift in the transmission. At that point, the truck seems to stick in the gear that it's in, and the gear indicator (1-6) on the display may not match the gear. In one instance I was driving 70km/h and the display was showing the truck in first gear. Other times from a stop, the gear indicator shows 1, but it behaves as if in a much higher gear, engine reving but no power to the transmission. Usually shutting down the truck and restarting clears the issue, but if warmed up, it does return somewhat quickly. I've also seen the gear indicator move between the numbers somewhat randomly and not in sync with actual shifts in gears. I've had the lead frame replace, and PCM reprogrammed, but the issue continues. The dealer is stating there's no new codes, however I have gotten the P0600 - Engine Code - which is listed as Loss of Serial Communication, but it is not logged when the issue recurs. Any suggestions on the root cause or methods to diagnos would be greatly appreciated.
Thanks
Dave