Lots of good info has been provided and you have to do the hard math to know what will work. But it is certainly possible. I used several 1500 series trucks (none as capable as today's) and towed 3 different fifth wheels for many years, miles and road conditions. And I would rather tow a fiver than a lighter TT any day of the week, no sway, no weight distribution or loading concerns (except loaded pin weight), more relaxing driving.
The single biggest problem is not exceeding rear GAWR which is almost always set by tire capacity. There are probably more 3/4 ton diesel pickups towing fivers than 1/2 ton gassers that are exceeding their GVWR and close to GAWR. But since they pull so well, owners may not really know their weight situation, especially if they aren't forum members. If your truck doesn't have LT tires, that would be an important change.
