OP even though I'm a gas fan...I would say go diesel since ur going to retire and wanting to move to a 3500. If u are going to a larger camper then it makes sense to go diesel. Now I will say that the newer ones will cost more then any gas truck over time. Get which one u want or need. I am a believer that gas trucks are lasting much longer now, diesels tend to have lost that edge with the new emissions. My experience only, we uses diesels everyday and the emissions are causing issues. If u go gas then any of the big 3 will work.