First off, all campers with slides qualify in the "very heavy" category. They start around 3000lbs dry, which eats up most of an F350 SRW's payload capacity.
Second off, if "get a new truck" is the appropriate answer to the question, then it is the appropriate answer to the question. A lot of times on this forum, people come on here wanting to do things that are physically impossible, or at least inadvisable, with the truck they have. Just because you just bought the wrong truck for what you want to do doesn't make it mean to tell someone they need a different truck. What's mean is allowing them to plow ahead blindly and end up with problems.