Once again USA Trains has come up with an excellent engine which comes in a variety of road names. You can get either a GP-7 or GP-9, Depending on the road name that you purchase. The primary difference is that the GP-7 units come with roof mounted air tanks, and the GP-9 units come with dynamic brake housings. In the prototype both units came with of without dynamic brakes, and the primary difference was in the placement of louvers. Also, the GP-7 had 1500 HP and the GP-9 had 1750 HP.
The prototype "Geeps" were used by railroads all over the country. Many of these units were equipped with steam generators and were used in passenger service as well as freight. They were first introduced in 1949, and are still in service (re-built of course) today. If you look at the short nose of your model and see a short stack and an intake vent, that is for the steam generator. My SP diesel came with this feature and I know the Santa Fe "war bonnet" unit also has it. I do not know if this is common to every unit, but I suspect for tooling purposes, all the shells are the same. Many of the prototype "Geeps" were painted in rather somber freight colors. USA has chosen the brighter colors used by some of the roads and while they might not be prototypically correct for freight service we will leave the topic and discussion alone.
There is some audible gear noise from this locomotive when you first take it out of the box. Over time, this noise diminishes, so you should probably break in your diesel in both directions. Aside from this gear noise, the engine runs very well and pulls well. It starts very smoothly and can be mu'd with the Aristo RS-3 without worrying about the units bucking each other. I will be providing miniature socket and plug connections on this unit so that it can share power pickup with the unit it is mu'd to. The engine handles rough track and minor debris with ease, due to the extremely flexible trucks.
Kadee makes a coupler conversion kit specifically for this locomotive. It is #785 and if you follow the Kadee instructions carefully you should have positive results. You may need a longer screw, since the original coupler screws in many cases are too short for the conversion. The coupler swing prevents the use of knuckle couplers on 2 foot radius curves and will probably give you trouble with the 1200 type turnouts.
USA has produced a highly detailed model. Many of the parts, such as air hoses, cut levers, and handrails must be attached by the modeler, which in my case means the use of a magnifier. I would recommend the use of Zap-A-Gap CA cement to secure all pilot details in place. Do not permanently glue the hanger straps on the truck side frames. If you do, you will have to break them to get at the side frame screws. Use photos if you are unsure about the location of details on the pilot. The instruction sheet is not real clear.
The dynamic brake pods are just sitting on top of the engine. Do not lift the engine by this part or you will have an expensive surprise. I have two of these units in Southern Pacific "Black Widow" colors and wanted to make the second one different. I purchased decals from Walthers and re-numbered one unit from the 7000 series to the 3000 series. I have not changed the number boards and will do this at a later date as this appears to be major surgery. I removed the dynamic brake housing and ordered the air tanks from Charles Ro. I then added these tanks to the top of the engine. The tanks as delivered were backwards for SP prototype and I had to redrill the holes to make them fit in the proper direction. I now have an SP engine which is somewhat prototypically correct. The SP fitted the tanks on top of some of their "Geeps" to make room for a larger fuel tank and the crews dubbed these units "torpedo boats". They were re-numbered from the 7000 series to the 3000 series.
Remember, this unit has the sliders that help in power pick-up. They will catch in the old Aristo turnouts and need to be removed or replaced with LGB pickup shoes. USA is supposed to be coming out with some sliders that are wider and will not catch and Aristo's new turnout frogs supposedly have been redesigned to help eliminate this problem.
Another word of caution. This engine comes with two sets of stacks, one plastic and one metal. The metal stacks are to be used if the smoke unit is to be utilized. However they have nothing to secure them to the shell and will fall out if the engine is turned over for maintenance or lubrication. Don't be alarmed if the unit smokes more out of the rear stack, this is normal per the instructions.
Back when there was a web site called LSOL (Large Scale On Line), there was a lot of discussion about the marker lights on the USA models. It appears that they are directional with the headlights and show green when running forward and red in reverse. Many roads ran green markers when the train was a "second section", some used yellow. Most white markers were displayed for a train running as an "extra", so in the "real world" markers are most often not lit. The LEDS that are used in the USA units for markers are polarity sensitive. (Positive current makes them one color and negative current makes them another color.) These can be changed out to white LEDS if the modeler wants. These white LEDS are now available through Radio Shack.
In all this unit is a great runner and scales out close to 1:29. It's excellent slow speed operation makes it great for switching with Kadee delayed action couplers. I will be putting wire connectors on mine for smoother Muing.