It will not increase the vehicles rated weight ratings or the registered weight rating. However, it will increase the carrying ability if the suspension is the limiting factor.
A friend of mine who had the same dilemma in his F250. He added F350 springs and track bars essentially making the truck identical to an F350 in the rear. Same axles, same brakes, same tires, same everything. Did it increase is rated weight? No. He would have had to send his truck to a final builder to get the sticker and GVWR re-rated which costs a lot of money. It did increase his actual carrying ability without squatting four inches when pulling his trailers. Although, here in Texas, you can register your truck for a higher GVWR so a 3/4 ton can legally carry what a 1 ton can.
Not saying that you should get a 3/4 ton for that trailer because I would get a 1 ton for that weight. Just answering the question.
