Trottle cut on upshift really slows you down, at least after my experience.
Bl2 for example, the lap after I turned it off, I beated my pb with almost a second -.- Well, of course, this was not only because of that, but I could see that almost all my lap after I turned it off, was faster than my old PB lap that I had struggled to get.
That was with RB4 btw.
The only thing that drives me mad is when you shifting, it`s like this :
wroooOOOOOMMmmm SHhhh wroo...
You get the picture, it sounds like hell, but goes a lot faster, at least in my case.