Mitsubishi Legnum 1.8 GDi Automatic Station wagon

After a quick search at

The problem is due to the lock-up mechanism in 4th and 5th gears not engaging properly. This is a design fault and is very common. The problem will happen when the car is under load (going up a hill) and you slightly squeeze the accelerator just as the gearbox is engaging the lock-up mechanism. The gearbox is also more likely to do it after a motorway run though it is hard to do it on demand. This problem really soured my early ownership of the VR4 since when I bought my car over 4 years ago, nobody knew much about it (including Ralliart) and hence I spent thousands before the problem was identified!!!!

There is a fix to this problem but unfortunately it is not cheap and cost me £1500. It involves upgrading the lockup mechanism and replacing the rear clutches.

or

Has been fixed by removing the centre console and ensuring that the gearbox wire connectors were firmly locked together.

or

Could also be a worn damper in the torque converter.

Hope you get it sorted mate.

(snipped)

Well this vehicle doesn't have a 5th gear, but what is interesting is that problem is at its most severe when the vehicle isn't under load. Going up steep hills or round bends - or both - doesn't provoke it, but get the car on a straight stretch of flat road and the problem really kicks in. The smoother the road surface, the more pronounced is the problem and it only happens in 4th.