Assuming that tire wear spans the entire circumference of the tread, I'd imagine the gold-plated next step is to visit a reputable body shop that has a frame rack and measure all the reference points accurately to make sure everything is within spec.

Throwing good money after bad money to fix the suspension & leak might not be the best use of bucks.

The cheap DIY is to get under there and visually inspect all the mountings, arms, and bushings for anything that doesn't look perfect. However, if the frame is bent slightly, there's no reasonable way of seeing that without the right equipment. This may put you in a position of chasing imaginary problems; all the things you can see look great, so there's nothing "to fix". But the frame isn't confirmed to be within spec.

I'm not overly familiar with the alignment process your truck would have had to get those numbers... and if it would have picked up a bent axle in that process. You could call big brand tire and ask them if the alignment machine would see that the rear axle is not within specification.