This is the second year with my F150. It is a 04 FX4 4X4 SCrewCab. I had a 95 Explorer 4x4 (selector for 4x4 was 2wd, 4wd auto, 4wd lo) I really did not to use the 4x4 last year but with the 12+ we had Sat i got to really use it.
the explorer in 4x4 auto I could not tell the difference when i was driving it RPM's did not change just had better traction. in the F150 when i switch it from 2wd to 4wd hi the RPMs jump up. at 50 mph in 2wd just above 1300 in 4wd hi 50 MPH I'm about 2000 and there is a whining noise. even when i switch back to 2wd the RPMs stay up most time till i park it and restart it. is this normal are the 4x4 systems that much different between the two trucks and how they work. i understand that the f150 is more of a truck but it does not sound right and i don't want to take it to the dealer for nothing.

 

could be that it disengages the over drive?? I am not sure why it wouldn't switch to od when changed back to 2hi.