4 year old under 40k miles that has started to have issues going through the gears. LRover dealer and computer can't finding anything. Oil in gear box has been topped up, surprisingly they said it has no leaks but was empty. Not happening on every journey. In 4 wheel drive, starts with putting foot on the accelerator to move off and nothing happens, it just creeps up to 2 mph, then start to get increase speen slowly even if you have foot right down, rpm surge then the gear kicks in. in 4 wheel drive this happens all through the gears and it won't go faster than 59 mps. RPM then go to 4000 lights/mesages start flashing and it drops to 2 wheel drive and goes like a dream. Some of the messages are stability control not avail/ 2 wheel drive/traction reduced. Any idea what it could be as the LRover specialists have no clue as the computer doesn't tell them