I have a 2008 f150 5.4 triton. Was driving on the highway with no issue whatsoever going about 70mph. Then there was a huge clunk noise and I looked down to see my rpms increasing and my speed decreasing. I pulled over onto the shoulder to see if I had any of my gears and couldnt move at all from a dead stop, or put it in reverse. I threw it in park and turned it off, then tried to crank it and I can't even get it to turn over. Tested the starter and went ahead and replaced it bc you could hear a bearing loose. But I'm stumped at this point. Could it be a neutral safety switch, a solenoid, or sensor in the tranny? No weird smells, fluid is normal, and no smoke. Can switch the column through all gears, nothing is stuck. Thoughts?

 

Any Maintenance lights, or DTCs?

 

the check engine light is on but my obd wasn't picking up any codes.

 

I have a 2015 3.5 EB, so different than yours, but I had a somewhat similar experience but it did throw a DTC that led me to replacing the throttle body, which did cure the problem. With my problem, I was able to restart the engine after turning the ignition Off, so kinda thinking your problem is different...

 

Have you looked underneath? Drive shaft or differential are possibilities. Put it in gear and see if the transmission output shaft (slip yoke) moves.