Auto transmission slipping

[brad]

Hi my auto transmission on 230sl 1965, has started slipping in all forward gears after driving up a steep hill and kick down utilised, Venturi / throttle switch &  transmission solenoid all good, will check modulator pressures next, The transmission has only done 1500 miles since rebuild but did spend two years not in use until two months ago ( last 150 miles).
Any thoughts, Brad

[ja17]

Brad,

Make sure that the transmission linkage is not stuck from lack of use. 

[brad]

Thanks Joe,
The linkage seems ok, I've just removed the pan & filter no signs of debris in the oil, after replacement and top up I'll check the modulator pressures, Is the test point the 12mm hex head plug forward of the modulator in the bottom corner of on the transmission body?

Regards Brad