A listing-first buyer guide for separating pickups from chassis cabs, choosing gas or diesel, deciding between SRW and DRW, and avoiding expensive towing-spec mistakes. A search for a Ford F-350 for sale can produce two trucks with similar badges and completely different purposes. One may be a crew-cab diesel pickup built to tow a fifth-wheel trailer. Another may be a stripped chassis cab waiting for a service body. A third may be a luxury Platinum…