Joe Strapac, in his Southern Pacific Historic Diesels, Volume 8, mentions that the V12-244 engine in the RSD-5 simply could not take the punishment of 24 hour days on Tehachapi; they were spending too much time in the shop for engine repairs. Espee would eventually ship 21 tired RSD-5's to Alco & receive 21 new DL-702's (with V12-251 enignes) in return.
Many early buyers of Alco PA/PB's, including Santa Fe & Espee, suffered problems with its' V16-244 engine, including flexing & cracking of the block; early engines with a GE air-cooled turbocharger were also problematic.
Finally, Espee had to deadline all its' C-630's, when only 2 years old, due to the V16-251 engine eating pistons. Alco replaced the pistons with steel - capped ones under warranty, with 2 results: Alco's net profit on the units went to zero, and Espee never bought another Alco road diesel. Joe Strapac also theorized that Espee was so used to EMD locomotives, that both Alco & GE's products suffered by comparison.
I've also read of Santa Fe's experiences with Alco C-636 demonstrators failing on their first TWO runs. Not the way to sell diesels.
So it seems that Alco's quality & reputation suffered at the same time that EMD's improved. Strange then, that Alco's Canadian branch, Montreal Locomotive Works, would continue to build road diesel locomotives for various customers through the 1970's.