Best to go here;
http://www.n54tech.com/forums/forumdisplay.php?f=16
Grab a couple of 4th gear runs through the RPM with the JB4 interface connected and logging on... You will get someone smart to review the logs and point out issues
Even different brands spit out vastly different numbers. I guarantee different dyno's of the same brand have different variances of calibrations.
Run multiple dynos with adequate cool downs between stage1, stage2 map 2 map5 etc with the same tuner/dyno..