The other day I went to get some fuel. When I unscrewed the rear gas cap ( the side tank had been removed before I bought it) a tremendous whoosh of air came out. I put in $20. Then took off about a half a mile and it quit running like I had just turned the key off. I pulled off the road an tried to start it but it wouldn't. So I walked home. In a few hours I went back and it started right up. This has only happened about once a year., not often. The truck is very dependable but only a weekly driver. I always fill up though but only got 20 this time. I don't know why it would do this. I think it obviously loses pressure somehow. Then it pressurized itself after an hour or more. I don't know if the side tank being removed has something to do with it either.

 

Never had a dual tank system but guys have talked about the yank selector or switch going out.