ML320 gear change problem!!

[sky]

Hi I have a 1998 ML320 Auto. Recently my ml has been getting stuck in 2nd gear, this only seems to happen when the car is at normal operating temp. If I drive 50 miles without taking out of drive I dont seem to get a problem. But if I go on a 10minute drive, stop the car then start to drive 5mins later sometimes it will pull away in 2nd gear and wont change gear unless I come to a standstill where it engages neutral, I then pull away again and it will be fine. I can tell when this is going to happen as it really slams into gear when i select drive, so I know before I pull away it will stay in 2nd. It has just been into the garage for replacement transmission and sensor. This hasnt solved the problem although the garage says the fault hasnt occured again since they hav had it back. Im starting to get very worried any ideas greatly appreciated. Thanks