Mike,
Yes I do have some recent 6-axle Premier diesels with the 3/2 system, they're all SD45T-2s, (scale wheels), and they're actually amongst the smoothest running engines I have. None of them exhibit the same trait as the SD70ACe, so I have my doubts it's the 3/2 system itself. It's not sluggish or jerking behavior that's being experienced. It's just a constant cycle of drifting to a near stall then rapidly accelerating (surging) back up to original speed repeatedly when pulling heavy trains until it's at or above 8 SMPH. It's like it's having difficulty self-regulating at those lower speeds. It's not from a lack of track power (I use a Z4000 with both posts powering isolated loops on an 8X15 layout and use auxiliary transformers for buildings/accessories). There's no gear binding that I can detect either. I'm a bit perplexed with this one, and it's a bit frustrating if not annoying.
Having said that, and along the lines of your comparison between the early PS2 engines and the more current ones from approx. 2007 on, what I have noticed is that the earlier PS2 engines do indeed appear to have better operating slow speeds below 4 SMPH than the newer ones. I have a few of the early PS2 Dash 9s, and I can get pretty decent crawling speeds without any jerking between 2-3 SMPH. The latest ones however, at least from my own observations, only seem capable of this at or above 4 SMPH. Main difference is that the early PS2s are 5 volt and the newest ones are 3 volt.
But then again, maybe the sound/personality files being used is contributing to it? Now that I think about it I have one early PS1 Premier GS4 Daylight engine converted to PS2 (3 volt) and the original sound file downloaded could crawl decently between 2-3 SMPH, but it lacked the crossing grade feature so I tried a more recent GS4 sound file and got the crossing grade sound sequence I wanted but then I noticed that it was more jerky between 2-3 SMPH than the earlier sound file, go figure? As far as I know the wheel diameter and gearing hasn't changed in the reissues but I could be wrong.
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