I wasn't aware that they named freight trains in the way that they named passenger trains.
The Northern Pacific Railway was one railroad that operated through Miles City in the 1950s. The NP named their southern Montana passenger train the North Coast Limited.
When Amtrak operated that route they called it the North Coast Hiawatha.
The Chicago, Milwaukee, St. Paul, and Minneapolis Railroad (aka "The Milwaukee Road") also passed through Miles City in the 1950s. Their passenger train was called the The Olympian and later The Olympian Hiawatha.