I can relate 100%! Here's my obscure theory. The frontal lobe of the brain is responsible for higher level functioning such as memory, logic, etc. ADD brain scans show "holes" in the activity of the frontal lobe of the brain affecting higher level functioning. So without medication us ADDers are expirencing more primal/survival brain function during a competition. Sort of a "win-or-die" mentality. Physiologically our brains are not using the reasoning area to it's fullest capacity. So when we take our medication, the area's that were previously off are now turned on and we function much closer to normal. We don't go into the more primal "do-or-die" mode as rapidly because the logic/ reasoning/ memory area of the brain kind-of says "oh, yeah, this is just a game, I remember that nothing bad happened last time I lost. I'm just going to have fun". I think some of that drive... or maybe... need to win is irradicated with the brain's ability to fill in some of the previous "off" areas or holes in the frontal lobe activity. It isn't such an urgent survival request when we compete.
So theory aside, I used ride and compete in the equesterine hunter/jumper division. I was a disorganized fool and a bumbling mess of forgetfulness and nerves before every single compitition. Once I was in the ring I think I entered my "win-or-die" mode. I felt every muscle, I was aware of every movement and twitch of my horse, the saddle below me, the audiance, everything. I was a great rider, but I had to be. I needed to win. For financial reasons I gave it up but I think I may have died fom the stress of the meets!!!
I have a much easier time prioritizing and realizing that loosing is ok and it does not make you a looser. I don't know if medication would have drastically changed anything while competing. While on medication, I don't really feel much of the drive to participate in competitions any more.
So to make a short story long..... I think maybe cutting back on the dose may give you just the advantage you need! Tell me how it goes, I'd be interested to find out!