It was designed for 2 ft (610 mm) narrow gauge and is the largest two-foot-gauge diesel–electric locomotive in the world at a maximum weight of 48,000 kilograms (106,000 pounds).

[3][4] GE's usual practice was to attach locomotive builder's works plates to the unit's frame below the cab.

[3][5] As a result of the severe clearance problems presented by the two-foot gauge, it was not possible to follow the usual practice of axle-hung traction motors.

[5] Over the years since the Class 91-000 was commissioned, the demand for rail services declined steadily on both the ACR and the Langkloof lines.

[6] Despite this, in the Avontuur Railway's centenary year in 2003 Spoornet still stated its commitment to keep the line in service by undertaking to invest in infrastructure and technology.

As late as September 2005 there was even talk of extending the 107-kilometre long (66-mile) branch line from Loerie further into the Gamtoos valley to assist farmers who had difficulty moving their produce.

[5] However, Transnet Freight Rail (TFR) had decided that narrow-gauge railway operations were no longer in its "core line of business" and began putting some of the locomotives up for auction.

The rest of the fleet which were still on the TFR roster were standing idle, staged at the narrow-gauge depot at Humewood Road in Port Elizabeth.

Five locomotives were sold to RRL Grindrod, a joint venture between Solethu Investments, a South African Black Economic Empowerment (BEE) rail logistics company, and Grindrod Limited, a shipping and logistics group, for use at Welkom in the Free State to haul mine hoppers.

Four of them were renumbered in the range from RRL 91-01 to 91-04 and their original narrow-gauge bogies were cut in half and widened to 3 ft 6 in (1,067 mm) Cape gauge.

By April 2017, both 013 and 018 were in storage in restored condition inside a section of the Humewood Road diesel depot, for sale.

However, with the Apple Express losing their leader to Covid and failing to win a tender to operate, 91-005 reverted to the previous owner and was sold to the DRC (Congo) in August 2023.