[Fosters]

you are increasing the speed at which you're spinning your transmission and rear end assembly by upping your gears, therefore the resistance is higher = more drivetrain loss. you will be dynoing lower.

You are also multiplying your torque by a different amount (4.1 instead of 3.55), but the dyno takes that into consideration; they will ask you what gears you're running.

dynoing an auto is the best thing to see this... it's very common for them to be dynoed in 3rd, where their 1.0 gear is, however, they can't hold that gear at say, 40 mph/2000 rpm to start in it, so they will end up inevitably starting in 2nd, and getting a good upshift, then keep going into 3rd till redline. 2nd gear is usually at the beginning of a dyno of an automatic car, and you'll be able to see it as being quite a big jump at the beginning (50-100 hp) then the regular dyno graphs show... basically 2nd gear on an auto is what would happen if you don't tell the dyno operator that you've got 4.10s and he keeps the 3.55 ratio in there. it'll show that you're making 600 hp, but your dyno will end at 3500 rpm :p