from what I've seen in my many dyno's - the car doesn't put out the top numbers until its 4th or 5th dyno run! believe it or not!
If the power continues to go up after the second or third run, ask if you can continue on until its stag or goes down.
2 runs goes by in less than 10 minutes. Takes longer to hook the car up on the dynowheel and tie it down...