I'm running same truck as you, standard 3000 b&w companion, on furthest back setting and will be pulling a sabre in about a month.
You cant get 90° but close. I would guess 70-80° but im not positive, I get to technical to ball park guestimate any more than that. Have tested some at my dealer. And I wont ever even crank a camper 70° myself, its too hard on axles, tires and such.
Now an empty gooseneck equipment trailer.... yeah I crank those pretty hard sometimes, only empty though.
MillerTime- Future Sabre Handler!!