The caster is low for some reason... springs settled a bit? The pinion angle may be off as well and the shims may even help.

If the springs are reasonable, I'd go ahead and shim it to specs. It will take a fair amount of shim but I'd go ahead and do it. If you do have vibration you can always back off on the shims... but I'd be surprised if you do. For the shims, aluminum is frequently used... but not recommended as it can break down with the high loading it gets. Steel is better.

Also, for stability, you might ask that toe be set with more toe in... within specs but more than what you have. Toe in compensates for the drag of the tires stretching the tie rods and other stuff... with bigger tires, more drag so more toe in. More toe in usually increases stability.