digitrax drop in decoders that i have installed in my locos have always been a little loose when i put them in. i have had to add a little solder to the contact areas where the decoder picks up power from the frame. when i installed decoders in a pair of LL proto rs2's. the first one i did worked good with the shell off. but when i replaced the shell the decoder moved a little and caused a short damaging the decoder. i called digitrax and they said to return it and they replaced it with a new one. the second decoder i added solder to it to tighten it in the frame. do you have the digitrax decoder tester. it will show if the decoder is reversing power to the motor. give them a call instead of an email. it's faster. i had to call them yesterday and the tech man was very helpfull with the info that i needed.
Number one, Turn off DC Support. It might be your problem. Symptoms are run away train. I learned that one the hard way. Some programmers have it in their menu's. If not the CV is part of CV29. The digitrax has analog operation ON by default. Should be turned off.
Also start over by setting CV8 to 8 to reset the decoder.
Springfield PA