lacks power, backfires, at low rpm, runs perfect at higher rpms' - help

[808Ducati]

2003 620 with 20K on it.  Started running really rough, backfiring, no power at low rpm's all gears when driving, but at higher rpm (above 4000-5000) runs perfectly, and when standing, runs fine even at low rpm. 

plugs are fine.
engine oil is fine
air filter is clean and airways all clear
gas is new
removed and cleaned up the carbs (they were fairly clean to start with)
replaced the injectors

Still have the problem.
Need help identifying the problem:
Fuel pump?
Something funky about this bike's fuel delivery at low rpm vs high rpm?
Thoughts?

[Speeddog]

My first guess is your throttle position sensor is bad.

[desmodoktor]

My first guess is your throttle position sensor is bad.

how can we test the TPS?

[Speeddog]

You can get a general idea of it's condition by checking resistance with an ohm-meter, checking for a smooth progression of resistance fron closed to wide-open throttle.

[desmodoktor]

You can get a general idea of it's condition by checking resistance with an ohm-meter, checking for a smooth progression of resistance fron closed to wide-open throttle.

thank you! 

[OT]

Less likely, but check that your header bolts haven't come loose.

[ChrisK]

I'm a bit of a noob to this kind of thing but could the ignition coils be going bad?

[rule62]

I also think a TPS check/reset is in order. There are some excellent instructions on Brad Black's website bikeboy.org. All you need is a multimeter capable of measuring down to 150 mV. I did the procedure on my '04 620 and it resolved some similiar issues.