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The main/tail shafts are different, so requires a full tear down to convert 2WD to 4x4, or visa versa, to change shafts
I think all 4x4s had a deeper pan, for better cooling/more fluid
Internally 5R55E parts, except for shafts, are the same, 2WD or 4x4
There were changes over the years, these changes would be year specific
1997-2000, were the same overall
2001-2011, saw a new ISS sensor added, needed by 2001-2011 PCMs(computers), so you could put a 2001-2011 5R into a 1997-2000 4.0l Ranger, computer just ignores the ISS
But you can't put a 1997-2000 5R into a 2001 and up because computer needs the ISS signal, which is missing and can't be added to older version
55E means it has a bell housing the fits a 4.0l V6 engine, OHV or SOHC
44E means it has a 4cyl(2.3l Duratec, 5R) or 3.0l Vulcan V6 bell housing