Vuaxhall insignia automatic gearbox

[Mdrwtt]

Hi guys my vuaxhall insignia 2012 in 2nd 3rd 4th gears going up the gearbox it's like it's over reving abit Before it changes when the cars In 5th gear and it changes down into 4th gear it's like a thud of a gear change but after about 45 minutes this thud turns into a double thud of gear change also after about 45minutes of the car running and the car stops in traffic the gearbox goes into neutral when it goes back into drive it thuds 1st gear do you guys think this could be valve body thanks mark