Hello Torre,
DAQmx is in fact more efficient than Traditional DAQ, so this behavior you describe shouldn't be the rule. I haven't been able to debug/check thoroughly your code, so here's what I suggest:
a) Try the W2000 option to give more time to background processes (see this link).
http://zone.ni.com/devzone/conceptd.nsf/webmain/28A6979ECA9A0CAF862569050053D92D?opendocument
b) Try with the LabVIEW supplied DAQ examples which do a similar task and test/compare their performance
c) Check with the LabVIEW tools where the time is spent (Profile VIs tool)
Hope this will help !
Regards,
JorgeM.