Dump trailer rear(both) axle locks up.

The one's I see come in here are usually hub piloted drums put on bud hubs. The holes for the studs are much larger than the studs. Although the studs are not supposed to center the drum anyway will you post a pic of what you find. Maybe even a part number if it's good. Thanks.

 

Your drums clearly look like the wrong ones. The pilot on the hub is too big.
You have a big gap on the bottom and not on the top..

The hole size on studs is irrelevant as it's the hub that centers the drum.

Get the correct drums on there and your pulsation and locking up will go away.

 

I believe the drum center hole should be much closer to the shoulders on the hub, even on your old drums, and centering sleeves should not be necessary. It is possible it has been ran with a loose wheel and worn down the hub but highly unlikely on two or more hubs.
There are numbers cast on the hub near the hub cap mounting bolts. It may also list a MFG like Webb. With that, the diameter and width of the shoes a good parts guy should be able to get you the correct drum. I would not over look the possibility of a different set up like Grape said I just never saw them with your application.