Trailer braking is weak... maybe?

[bryancass]

I do not se in your list of references the only one that matters
That would be the manufacturer’s manual for your axles

https://www.carry-ontrailer.com/wp-c...xle-Manual.pdf

Page 7:
1. Place hub, bearing, washers and castle nut back on axle spindle in the reverse order from which they were removed. Castle nut should be torqued to 50 ft.-lb. Hub will rotate during this process.
2. Loosen castle nut to back off the torque.
3. Tighten castle nut finger tight until snug.
4. Insert cotter pin. If cotter pin does not line up with hole, back castle nut up slightly until pin can be inserted (Fig. 4).

[huntindog]

https://www.carry-ontrailer.com/wp-c...xle-Manual.pdf

Page 7:
1. Place hub, bearing, washers and castle nut back on axle spindle in the reverse order from which they were removed. Castle nut should be torqued to 50 ft.-lb. Hub will rotate during this process.
2. Loosen castle nut to back off the torque.
3. Tighten castle nut finger tight until snug.
4. Insert cotter pin. If cotter pin does not line up with hole, back castle nut up slightly until pin can be inserted (Fig. 4).

OK , good. Don't over think it. The little bit of play that will result from this procedure will go away when the components heat up and expand.
Intersting though, this manual doesn't give the spec for measuring play with a dial caliper. I know I have seen it in the past.