The big issues for the D58 was not having enough adhesive weight for a tractive effort of 55,008lbs, and retaining three cylinders, a concept abandoned by US builders by 1930 due to the much higher cost of maintenance. At a time when cheaper diesels were becoming available, the D58 design needed to be cheap and practical to run, and it wasn't. The way I see it the designers should have adopted one of two choices...I have no argument re the technical aspects of the 58cl, however what it highlights is that many crews worked them out as to how to drive & fire them, bringing them up to a fair standard.
1. If the tractive effort was more important, then the adhesive weight should have been increased to at least 223,850lbs. A two cylinder D58 built to that standard would have had cylinders 23.5x28, boiler pressure of 255psi and a tractive effort of 55,860lbs.
2. If the adhesive weight could not be increased (most likely) tractive effort should not have exceeded 52,455lbs for the 212,000lbs on the drivers. This design could use a pair of cylinders 23x28 with a boiler pressure of 250psi.
Hard choices needed to be made during the design phase, and ultimately the compromises made were the cause of the D58 debacle.
A similar situation existed on the Short South when the 36cl had their load increased to haul the same as standard goods, 59 & 38cl. No where else in the state did that occure, when considering it with the western working that occasioned the so called 75% load for most general goods trains on the Lithgow - Oge section, meaning standard goods engines were reduced in loads by 25% to that of a 36c but ran up the grades at the same running times as a pig.
On the South, also when the big engines were running, they both took the same load of 900 tons, but garratts, were only allowed 100 tons more than the standard goods engines when they had the old short coal bunkers, as the bunkers were increased they took the same load as both big engines.