Being a VK auto your transmission should be a Trimatic.Now you said you had the valley cover replaced,I assume that you mean the inlet manifold here.At the back of the inlet manifold is a fitting which is for a vacuum line that runs from your transmission.If this line is not fitted you will have dramas shifting gear thou you should still be getting at least one.I forgot to connect this line once on my old HJ 253 auto and it had me stumped why she would change from first to second but not top gear.Also check your transmission fluid level with the motor running and hot,not when it is turned off.You need the torque convertor spinning and full of oil to get a true reading.When the motor is turned off the fluid runs out of the top half of the convertor thus showing an elavated reading on your transmission dipstick.

Hope this has been of some help.