Top End Miss

My guess...either the gears are accelerating the car so much better the springs cannot keep up (my first guess) or your running out of fuel...or BOTH!

If you do not know what your spring pressures are...THIS is what's most likely wrong.

However, you may have a fuel volume issue as well. You could easily try larger needle/seats and raise your float level noticably...this should change something even if only 100 or 200rpm. If nothing changes at all, then I'd look at springs. This is truly what I think is wrong.
But I could be wrong too ;-)