Part of your description makes it sound like the dcc booster isnt powerful enough. The system you describe is a 5 amp system. It could be the booster is cutting power due to a sensed overload.
When I tried my MTH dcc out on an NEC 5 amp system, it did the same thing. Occasionally it would start up, but any movement commands sent the NEC booster into overload mode. Sometimes the engine wouldnt respond at all.
Once my NEC10 amp system arrived, everything worked perfectly.