My 7500 pound morbark has a 7500 pound torsion axle under it. The axle is always maxed out. I think the long term fix is a new axle or even 2 of them. ..
If it's a torsion axle with compressed rubber rolls, the axle may be not bent : the rubber rolls compressed in the main tube take permanent deformations from heavy loads. The connecting rod becomes no more coaxial with the main tube and the arms holding the wheels slightly rotate sideway, giving a look of a new born horse with spread legs. The tires don't like that at all.
You can change the rubber rolls yourself, hard job but doable.
The arm's connecting rod is just inserted between the rubber rolls, nothing hold it in place except the rubber's friction. So with a hard pull, it can go out.
It's way easier to gently torch the tube to soften / burn the old rubber. It doesn't smell very good though, but who cares?
Clean the mess, put halfway in place the new rubber rolls with some pasty soap as a lubricant, place the connecting rod and the arm in the middle and push.
I mean PUSH. Hard and well in line (not so easy).
Drive it in place to make the arm nearly touches the tube. That's all.
The trailer shops do it this way.
I made it on a boat trailer. It was only a 1500pounds axle though.
I used my cable puller, some slings and two trees in my backyard, a bottle jack and some home made clamps to hold it.
The trailer look way better after that and got again a good suspension.