The SD90MAC, like the SD80MAC, SD70ACe, and SD70M-2, has a wide radiator section, nearly the entire width of the locomotive, which along with their size makes them easy to spot.

These locomotives were informally designated SD9043MAC by railroads that purchased them with the option to re-engine them with 6,000 hp (4,470 kW) engines when they became available.

In 1996, Electro-Motive Diesel entered full production on their 6,000 hp (4,470 kW), 16-cylinder H-engine, and all SD90MACs made from then on used that for its prime mover.

Since the SD90MAC-H had such a large prime mover, it didn't offer the same operational flexibility as smaller units, limiting its possible customer base to only the largest railroads.

Also, since the H-engine was a new design, it hadn't reached the same level of reliability as EMD's previous engine.

Electro-Motive Diesel also tried offering a lower-power version of the SD90MAC with a 12-cylinder engine called the SD89MAC, but none were produced other than the prototype.

These units were reportedly capable of meeting the EPA's strict regulations and began delivery in the latter half of 2007.

These units, in the 8900 series will be removed from storage in Denver, and will be sent to East St. Louis, Ill., in small batches to be dismantled.

Canadian Pacific's SD90MAC locomotives, numbered in the 9100-9160 series had been in long term storage in Winnipeg, Manitoba, for much of the 2010 decade.

In September 2014, Norfolk Southern purchased 100 4300 hp SD9043MACs from Union Pacific with the intent to rebuild them into SD70ACUs at the Juniata Shops.

The last 4 SD90MACs were taken delivery by Norfolk Southern on October 3, 2015, running parallel to Western Avenue in Chicago, IL.