Cutting out

My truck starting missing on 2 cylinders then it will start to eun perfect on all 6 cyl Ive changed the plugs, wires, coil pack, cam and water sensor with no results. When it starts running on 4 you can put the truck in nuetrul tiurn it off restart it and it will run on all six for a fe minutes before starting missing again. Can you please advise me on what steps to take to find the solution to this problem'

Roy T Gardner