2003 Ford Explorer fix P0735 solenoid

That code can be caused by other issues besides simple solenoid malfunction. Internal issues such as damaged friction materials, stuck valves or the engine rpm being higher or lower than expexted for that operation range. This is one that I woudl suggest taking to a trans shop to have troubleshot. They have the scanning equipment to command certain gears on while measuring voltage/resistance across other solenoids to be sure that the root cause is actaully the 5th gear solenoid and not other internal issues.