help...desperate!

Hi all hoping somone can help as i need a solution soonest as the disco is my life boat emergency call transport.
td5 2000 es auto.
Just had the box changed. Local guy who is good fitted me a box from a 2004 model. Supplied by equicar 4x4
Now the damn thing will not go into overdrive.4000rpm at 45mph. also when selecting the sport mode the M light comes on
Can any one advice please.
shaun 07761091734

Sounds like the Hi/Low box switch is reporting the wrong way round, so the car thinks it's in low range all the time. That would explain the M as that is what you should get when the box is in low.