Grumpy_Mike:
Quite honestly I don't believe you are making those measurements correctly. They are stupidly small ammounts of current for a slot car to take.How are you physically making the measurements?
My reading of the data sheet is that the maximum current through the wiper is 2.5mA, this is way way too low to do what you want to do. You have probably blown the device and you are measuring something that is broken. A current of 2.5mA is not going to power your slot car. The whole design of what you want to do is wrong.
I would agree with you if the design of the PCB has the power driving the slot car going through the controller (n the Wikipedia page of slot cars there's an abstracted diagram that suggests as much (check the image here)), but I don't think the schematic of my slot car product works that way.
Here's how I measured the amperage:
