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When in neutral and idle your engine cuts out two cylinders, one from each bank. There is a switch on the bracket next to the end of the shift cable at the engine. Are you having a particular problem other than this?
You need to do a spark test of all 6 cylinders. 2 cylinders are disabled in neutral. If you have lost one or even two other cylinders then you will have problems like you describe. If you rev the engine too high in neutral the ECU will further cut cylinders with over rev protection.
You can get a spark tester at any auto parts store. Do the test and post back which cylinders are not firing.
The switch disables the cylinders to save fuel at slow speeds.