My T5 LWB manual has a problem with first gear. Forgive my non-technical explanation....

When taking off from a stationary position in first, it will often pop out of gear with a bang. Sometimes the engine will stall, and other times I can hear metal on metal as if gears are trying to find each other.

Is this something anyone else has encountered, or should I take it to a dealer to diagnose?

The van has done 270000kms...