UP/MP GP-15-1's


New member

So I had a couple questions about some of the detailing on these prolific yellow work horses.... There are somewhere between 4 and 8 of these things up here in Seattle (Though its more then likely there are a couple that move between Seattle and Portland or some such), and they have a few different sets of "Details". They are ALL equipped with RCL (Remote Control Locomotive) gear though. They're commonly seen switching Argo Yard or doing one of a couple daily runs down the Marginal Way Spur South of Argo.

First question: 2 Exhaust Ports vs 4?
Now, I know *most* of these units only have 2, and *most* of the ones I've seen only have 2. However, I saw 2 that were coupled together that had 4. Further, RRMods makes not one, but TWO distinct units with this configuration, though I wasn't able to deduce which of the listed 150+ units they were (I forgot which numbers they were when I saw them, this was about a year ago and I didn't write the Numbers down).
RRmods Page for one of their units:
And I would agree that was probably accurate for a MoPac unit w/o RCL, the Stacks at least are very close to what I saw.
So, my question. WHY are there 4 stacks? And why do they have these little black lifters on them? I can't believe those are spark arrestors?

Second Question:Different RCL Packages? This is for the Rivet Counters.
I noted minor differences between the RRMods RCL units and the RCL Packages on the GP-15s up here. Upon further research on RRpics I noted that the units that have the style RRMods included seemed to be predominately on the eastern side of UP's system, where-as the style that I see around here seem to be all the units on the west side of UP's system. Does anyone know why this occured or if theres any significant difference between the two styles? Its entirely possible that "East" vs "West" doesn't matter a jott and I'm just seeing newer system vs older or some other delineation, but whatever the difference is, I'm curious about it.
Eastern Style:

Western Style:

Thanks for reading if you have,