2 problems I can see from what you've said. Firstly they did the run in 3rd gear. You are correct in thinking that it should be done in 4th, and doing it in 3rd has let to inconsistent and under read numbers. Secondly, at the top end, your car seems to drop torque quite rapidly, more than I would expect. For a rev up engine, it should be producing power for longer, and if you follow the graph trend up another 500 revs or so, it would have put you in the right power range. This could be because of how they strapped it down, or because they did it in 3rd gear. When in the car, does it pull hard right up the redline? If so, I wouldnt worry about it, its probably dyno operator error