Most of the large V6 engines have a shift assist switch that causes three cylinders to shut down when shifting down from forward to neutral. If it is not set properly the motor will idle too slowly to handle the drop in power and will cut off.
Look behind the shift lever on the engine and you will find the switch.
If you temporarily disconnect the black ground wire on the switch it will disable the feature so that you can tell if that is contributing to the problem that you are having.
Be careful, without the switch it is more difficult to get out of gear.
hi thanks , will try that and get back to you, makes sense as when i start in gear idle also happens, ( yes overided start in gear just to test ). tvm.