Do you keep the scan tool connected as the engine goes into closed loop operation? If so what happens to the LTFT's at that point? I have an occasional DTC showing one of the catalytic converters is not within spec or threshold of efficiently. I'm told that can be due the sensors themselves or the cats are beginning to fail. FWIW I have about 165K miles on an '05 E350 with 5.4 motor.
The engine has just about 20K miles but the exhaust system is factory original.
When I watch my Fuel Trims I seem to run a bit negative while in the LTFT's, STFT's switching as they should.
I would maybe run your data again while driving, coolant warm enough to open the thermostat.
Also here's a video I've found very informative about Fuel Trims---this guy is one great teacher!
If you're not careful you can spend a lot of time watching his presentations!