2-8-0 Consolidation type locomotives moved most of America's shortline and branchline as well as a goodly portion of mainline shorthaul freight for half a century.   577 is a medium sized Consolidation with small driving wheels so she has a lot of tractive effort but not a lot of speed.   I'm confident she could handle a reasonably sized train of modern style "lightweight" passenger cars, and that's about the only kind there is in working order in Alaska.

I've ridden behind Southern Railway's 630 also a medium sized 2-8-0 with ten or twelve cars behind it, and the Southern has some pretty steep grades in North Georgia and the Carolinas.   I've been behind their #750, a light 4-6-2, with 12 cars pulling up the 18 mile grade out of Taccoa, GA that is close to 2%.   She was down to a cylinder stroke at the time and throwing chunks of coal 100' in the air, but she did it.

The early diesels that replaced engines like 577 were little if any more powerful, they just required less service.