Won't that cause you to lose a lot of power up top? I was just wondering because I am also about to put a 2 step on my car with a single 76mm and want to build boost on the line with but not lose power up top...
No it has no affect on power up top. You are only pulling it out for the load range that the 2 step is on typically 1.3-1.7 load above 5k. When you are @ WOT you are at 2.0 load so you are outside of that range where you are pulling timing.
From my understanding it won't affect anything at WOT due to the load being different. Only thing I was told was when my tuner changed things, it was going to affect the driveability some and make gas mileage worse.
No rain, heading to the track.
If he did it correctly it will not affect driveability or gas mileage. If he set it to -5 across the board for 1.3-1.7 in all RPM ranges then yes it will, you only need to do it for 5k+