I've noticed the same thing where nt seems to "revv" for lack of a better term, just a single core. What I found to be somewhat useful is opening task manager and if you see the "revving" of just one core.. go under processes and locate Ninjatrader.exe >> right click >> set affinity >> select all cores >> then click ok.

Its usually set to all processors by default anyways, but i found that by just going through the process/motions of setting affinity each time you open nt it seems to balance out the revving from just that one core and sort of shares the load with the other cores. But then this could also very well just be a placebo effect...

or restarting your comp at least once everyday tends help and smooth things out a bit. And over time your comp, well at least my comp seemed to "adapt" to the settings and runs all cores balanced. hope this helps.. or just ignore if i've mistaken your question.