99 34ft fifth or 04 37ft fifth how much difference in towing

Not what I wanted to hear! I left out one thing about the 37ft trailer, it has three axles. Would that make a difference in the need for a dually?

Thanks for the information! If we were to buy a dually, would you recommend going up to a F450, and of course the other question is long bed or short bed!

Thanks again for your input!