I have a 124 240td 722.3? box with a kickdown problem it does not kickdown to 2nd, kicksdown to 1st or third OK

The car if driven 'normally' drives well, changes up thru gears somoothly using all gears.
When going slowly if you floor the accelerator it kickdowns to first and off it goes thru the gears as you would expect.
At higher speeds when in fouth it changes down to third but that is as far as it goes, it is allmost as if second does not exist in kickdown mode!
select it manually it is there and holds to max revs even if you put the selector back into drive

Fluid is clear and does not smell burnt

I am a tech but auto boxes are an unknown quantity, any that come in are sent to a 'specialist'!