IMO, traction and Firestone AT don't belong in the same sentence. Good tire for being a cheap tire but can't give it more credit than its due.
To the op, if you got 55kmi out of any tire, I'd just suggest buying that one again.
That's about 15k more than I've ever seen out of a LT tire, but I don't run em down to the cords. Once they don't have winter traction they get pulled. Then I don't have the gumption to put them back on in the spring and wring out the last of the dry hiway miles.
Most any tire will last a long time if you run em bald or near bald. Ok for highway and dry weather. Or if you can't afford new tires.
But if your vehicle sees 4 seasons and all roads then the tires become essentially useless after they get down to 4-8 32nds for me.
My guess is the hi mile guys run em to the wear bars. Those last few 32nds wear very well and don't go away near as quick a s the first half of the tread.