Was the car actually making 10 psi? These cars all respond differntly to each other based on mods, condition of parts etc, which is why Custom tuningis the best way to play with these cars. Although you may have put the 10 psi tune in, your car may have only been getting 8 for example in the top end. You have to also realise that power does not just come from boost alone, you have to optimize the air fuel ratio and more importanly the timing. The timing is where the power comes from, 1 degree can add more than 5 rwkw if done correctly, but can also damage things if too much is used.