I have an HO Loco with LOKSOUND installed. The Loco was running fine in the past but currently has problems. It has a address of 5005, when I run it it will throttle down in several spots on the layout then come back up and run to the next throttle down spot. It is not shorting. I did a CV8 reset and it seemed to run pretty much OK using address 3.
What DCC system are you using? This is a classic symptom of the same address selected on more than one throttle, so one is telling it to stop, the other is telling it to go.
–Randy