Seems to me like he was asking for help fixing his current bike, not getting a new one. Maybe you should read a bit closer next time so you get all of the relevant details.
In regards to the tranny, it sounds like the gears are not fully meshing, perhaps. You say you are mechanically inclined and have a shop manual, so you might want to open her up and look at the engagement dogs. i am not familiar with the bike specifically, but it will probably have these. They are what actually position the gears inside the case. In many bikes (and cars) they are made of plastic, as they do not get much stress placed on them. All they do is slide the gears along the shaft. They will, however, get worn over time, and so, after a point, they might have worn enough where they are not fully engaging the gear. This could possibly be a very load-sensitive problem. It could also be compounded by case pressure. This would likely explain why it happens sooner under acceleration, and definitely above 6000 rpm. That is one of the first things i would look at.