Look at peak torque and peak HP RPM in second gear and try shifting it higher and lower to see if it moves the results up or down on the shifts. Also don't forget about water, oil and all the other lubricant temps, cold oils will make less power than hot oils do, especially this time of year
Write down all the things you want to try, put the most important once first, also don't move the shifter out of high gear until the motor is idling
Trust me on that one, I bent seven exhaust valves by moving the shifter to quick once after letting off of the throttle on a chassis dyno, JUST ONCE
So far
Traction and wheel spin can laed to false readings at the rollers as far as RPM and true output 
No two dyno will read exactly the same as each other