Before you start, playing with the TPS.
Check the simple first, lack of power in the mid to upper rev range could be several things: -
1. Lack of fuel weak mixture
2. Lack of air rich mixture
3. Too much air weak mixture
4. Too much fuel rich mixture
5. Weak spark.
The ignition system on Fazers is pretty solid, the leads can fail as can the caps and where the leads join the coils, or a cracked plug. All of these are easily checked, inspect the leads/caps and plugs, if all cylinders are firing it's suggesting your issue isn't the ignition system, but it could be. Lift the tank start the bike close the garage door just enough to darken the garage DONT shut the door, don't go mad or stay in there too long, it takes minutes to do this. If you don't have a garage do it at night outside, rev the bike and look for arching across the caps/leads. You normally suffer poor starting with ignition system problems, which you don't mention so I assume haven't got?
Based on the information you supplied I'm doubtful it's an ignition problem.
You've checked the breathers and you say they're ok. This leaves fuelling and air as likely culprits, check in this order: -
1. Air blockage, check the air intake I've seen rag or neck warmers sucked into the intake which restricts the air flow in mid range riching up the mixture.
2. Check the filter they don't last for ever, this is easy just take it out and ride it, if it all ok fit a new one.
3. Check the starter plungers are fully returning on every crab when you release the choke, this has the same effect as above.
4. Check the carb diaphragms even a tiny hole will stop a slide from raising, this will give you a weak mixture.
5. Check the inlet rubber balance nipple caps these split/tear when being pulled off, sucking in air and weakening the mixture. The inlets rubber will crack but these are very rarely more than skin deep, often owners waste money replacing them for nothing.
6. Check the fuel line, start at the petcock the clean the filter, check the inline filter and check the pump run a pump test.
In my experience it's very rarely the ignition system but could be caps leads are the main areas to check, I've never had a TPS actually cause your issue, when they fail the bike just doesn't run as well. The same with carbs being out of balance they just don't all of a sudden go out of balance and unless they way out the bike will still pull in the upper rev range just not as well.
Good luck lets us know how you get on.