[Tannaton]

^^^^ That really.

Do you mean 2002 or 2012?

There is a specific process to correctly load the torque converter into the gearbox, which is turning it in a certain direction and pushing it into the gearbox until you see and hear it drop TWICE as two further sets of splines engage. That can sometimes involve 20-30 turns. If this is not done, the last set of splines that wont have engaged are the oil pump drive and the effect of that is the torque converter and oil pump are damaged and the box is stuck in third gear when in "D", it won't shift and will slip in reverse.

If the garage have made that mistake, then I would suggest they aren't experienced with this gearbox type and a specialist will need to sort it (at their expense).