Judging by your MP3, it doesn't sound as if you're actually using a marimba patch from Virtual Drumline. VDL contains sampled marimba rolls that, if using a template from The Write Score, should see your 3 slashes, then automatically make the necessary controller change to play back the marimba rolls rather than the repetitive machine-gun style roll you're hearing.
Having an issue with my marimba rolls. They're half notes (and dotted half notes) with three slashes. They're playing back like a machine gun. Thoughts? Is there a setting or something I should check? I've attached a sample audio file so you can hear what I mean.