Gooseneck fifth wheel and a flat bed. Help!

Sounds to me like I need to scrap the idea of using the K20 and drag the powerstroke out. From my measurement at a local RV sales lot, I need to stay under 30' regardless due to my shed. If I get over 30', not only will I be buying a camper I will be adding on to my shed also. That being the case it is a 1997 OBS ext cab long bed f-250 with the heavy service spring package and the 7.3 turbo diesel. It is bone stock, nothing ever done to it performance wise. Still has the stock intake and exhaust. I know I have had a combined weight of trailer and load at 14K behind it and I know that I don't want to do that EVER again. Just a little piece of advise and I am sure I am preaching to the choir on this one, do not let family talk you into hauling stuff for them. There was a lot of lost religion when I got home.