Another distinct possibility is that the dyno operator is a moron (common problem). It is possible that you are having traction issues on the roller. What was your tire pressure on those runs ? Was is high ? Check and adjust your tire pressure accordingly.
Many peeps don't know this, but traction plays a large part in a properly executed dyno, w/o it you will show lower than expected HP/Tq figures.

Good Luck

 

the guy was good, the rest of the cars that dynoed had about the right numbers.
the car wasnt "peeling" out on the rollers, they looked to be moving at the same speed