When I accelerate a little hard there is a thumping noise, but there is none if I do it slowly. I already changed the bracket where the wheels are attached, the differential was checked and everything seems alright. Somebody told me it might be the gearbox mounting, could it be?
Your trucks problem could be the grease that came from the factory on the slip yoke, it might need to be greased again and you won't hear that thumping noise again, that happens with the Ford trucks with double cardan.