I would just sand it and cover with a high quality primer. I do not believe there is any need to strip the entire truck to bare metal. That would be a huge undertaking on a crew cab long bed!
When I was getting ready to paint mine the single stage paints seemed like a good idea because they are easier to touch up and I was planning to do the work myself. However, I ended up having it painted and the painter talked me out of single stage. He said the clear coat protects the paint from the sun and the paint job would last longer. So I ended up using base coat / clear coat. If you do a search their are quiet a few threads on single stage vs. dual stage paints on here.