This tip comes from a railroader out in California. His name is Greg Elmassian and he is an avid Santa Fe modeler. He loves to run passenger trains, and has a nice set of Aristo heavyweights which perform smoothly on videos he has sent me.

Aristo Heavyweight Passenger cars Tune-up
This is about the newer version, with the improved trucks and the details like grab irons that are blackened.
They come with underbody rods (I can't remember the right name now) and stanchions, but apparently these were not used on metal frame Pullman cars. I installed them at first but had to snap off an air tank to get them to fit. Turns out they are not on the Santa Fe prototypes.
Be sure to lube all the journals, these cars can have a lot of drag. I would also recommend greasing the truck pivot areas, they can be pretty stiff when delivered. These two things made a lot of difference in keeping them on the tracks.
OK, if you want them to run really well, then you need to re-gauge all the wheels. When you go to take a truck off, notice the red wire from inside the body is on the same side on both ends. All you really need to do is remember this. I put the car on it's back, remove the 2 small screws that connect the wires from the truck pickups to the wires that go inside the body.
Take the 2 screws and washers off and remove the truck, GENTLY feeding the power wires through the hole in the truck. These wires are normally poorly soldered to the lugs, and if one feels very flexible at the joint, you would do well to resolder them. On mine, the wires were not crimped into the lugs before soldering, and the crimp that is a strain relief onto the insulated part of the wire was likewise not crimped. Definitely a future failure point. Might be best to replace them with new ones properly crimped. Soldering is optional if you do it right.
Now, you want to take one side frame off. There are 2 screws on top, but the side frame is also glued on! Use an xacto knife and wedge it into the middle, and then open it up enough to get a small screwdriver to spread it open.
CAREFUL! There are bosses in the plastic that you can cut off, so keep the knife AWAY from the screw holes.
Now this will not be enough to get it apart, you need to use the xacto again on the ends. You can see where there is a locating peg about 1/4" in, don't slice it off! Just get the xacto in there enough to split it open enough for a screwdriver. PLEASE, be careful, don't hold it in such a way you will jam the xacto into your hand!
Once you have popped one sideframe off, you can tilt it away enough to get the wheels out. NOTE which side is got the insulated bushing, and which side the axle is metal to metal to the wheel. You want to put the wheel back the right way. The non-insulated side always goes to the bushing that has a wire to it.
This is a good time to lube the axles. I would use a plastic compatible grease with moly in it over oil.
When you put the sideframe back on, be careful not to pop any of the four pivoting ends (for journal motion) out of their pivots. Also be sure you do not pinch the wire between the sideframe and the rest of the truck. Rule of thumb: If it does not snap back together with light finger pressure, you are doing something wrong.
Once you have replaced the 2 screws on top, then check for the nice up and down motion of the sprung journals at each corner of the truck. I squirt dry graphite/moly lube here and work the journal up and down until they move freely. Fully 50% of mine "stuck" out of the box.
Before you put the truck back on, lube the area on the underside of the floor with grease, where the ribs on top of the truck ride.
Thread the power wires through the hole in the truck, and then screw the 2 pivot screws on. These do not have to be more than gently snug, nothing rides against them when running. Then attach the power wires with the small screws, making sure the red wire is on the same side of the car at both ends.
If you do all of this, you will find a marked increase in rolling performance and much fewer derailments.
The power pickup on the cars is weird. The center axle of the 3 axle trucks is not sprung, so does not pick up power well.
On each truck, the center axle picks up from one rail, the outer 2 sprung axles pick up from the other rail. Well this would be fine if the trucks were identical, but nooo.. looking at the way it's wired, one rail is only picked up by the 2 unsprung axles on both trucks, and the other rail is picked up by the 4 sprung axles. Weird.
Well, you can swap the wheels around and even this out. An easier fix is to take 2 cars, and swap trucks between them. Be sure you don't mess up the polarity when doing this.