Have you tested the motor and mechanism on just a 'dumb' DC power supply? That's a pretty massive current to be drawing if everything is operating well.
Here's an excerpt of a post I am working on for another decoder install, that describes a motor startup voltage and current draw test I like to do. Might be of some help, just to make sure you've worked out any mechanical issues or inefficiencies.
Motor start voltage and no-load current
One of the first tests I do on an engine once I get it all stripped down is a motor startup voltage and no-load current test. This can give a really good indication of any fundamental motor, geartrain, or linkage issues. (This is actually really easy to do just about any time you have the shell off, and is a good preventive check.)
I do this test using a benchtop DC power supply. Starting with the lowest voltage setting, I slowly ramp up the voltage and look for the point at which the motor just starts to turn. For a typical motor installed in the locomotive, I normally see startup at around 0.8 to 1.0V and 0.2-0.3A. If the voltage is much higher than that, something probably needs attention. This is also a good time to let it run just barely ticking over and watch for any irregularity in the motor speed or wheel speed. Any slight increase in drag will cause the motor to stall. If this happens at a consistent location, it usually indicates an issue in the drivetrain.
The key aspect of this check is that, unlike with the decoder installed, the voltage here is not feedback controlled. With the decoder installed and running normally, it will try to drive through increased load by boosting the motor voltage. While the engine may operate, this can mask issues that can lead to long (or short!) term mechanical and electrical reliability problems.
Then I ramp up to about 5-7V and look at the current. The motor should be humming along at a pretty good mid-speed pace at this point. With just the drivetrain friction, current should be in the 0.1 to 0.2A range. This is a good time to watch and listen carefully for any noise, vibration or rattling, which can indicate wear in gears, lack of lubrication, or minor binding in linkages and so on.
I do these checks in both forward and reverse directions by reversing the polarity. If the forward and reverse direction voltages differ by more than a couple tenths, that's another indicator. If there are multiple motors, I test each motor individually and compare. Again, the values for both motors in both directions should be similar.
In the case of this engine, I was a bit appalled when I measured a starting voltage of over 2.5V and current of about 0.7A! Clearly something needed help, and it didn't take long to figure out - the old gearbox lubricant was completely congealed around all the gears. After a complete teardown, cleaning, and reassembly with proper lubricants, the starting voltage and current were right where they should be, and everything was running really smooth. Another example - when I did my Lionel docksider a while back, I discovered that the quartering on one axle was off by one spline on the shaft, because the motor was stalling out at a repeatable wheel position.
