Folks,
I'm a professional mechanic by trade and I get frustrated when people describe a problem and the "suggestions" are merely shots in the dark that don't exhibit any type of diagnostic process:
The bike won't rev above 8k - is it "bogging" or "missing"
bogging, i.e lack of power WITHOUT an ignition misfire is usually related to a fueling problem. Check for the simple things first, a kinked fuel line, a bunch of crap in the fuel tank, etc. A further diagnostic for this is to perform a fuel pressure test. The bike requires more fuel when under load than idle.
Missing, i.e. an ignition misfire, is when the bike starts dropping revs and it is clear that one or several cylinders is firing erratically. This can be caused by several things, arcing wires, low voltage to your ignition coils, bad plugs. Initially, check the wires to make sure they are seated and not arcing.
Always check the simple things first - make sure the air filter is clean, check to make sure your battery cables are tight and the charging system is in good health.
Can you provide some more info as to when the problem started happening and what conditions under which it happened.
On these bikes, verifying proper TPS operation is important, too.