I too have experienced this, in particularly the sweeper at the end of our straight, I think it might have something to do with the boost being controlled by the throttle position, as you back off for the sweeper entry, and then apply only some throttle it cuts the boost back according to the throttle position, normally i run with about 10% drag in mod and reducing it to 5% did not make any difference, what did help was if you stayed a little more on the throttle but then you cant hug the curbing on our sweeper, but that did eliminate the odd feel

I am going to try this awesome speedo out again to day after work to see if i can eliminate the slow down/odd hook it develops in our sweeper

hope the guys can shed some light as we have a club race this weekend