Slight misfire/hesitancy at 2000rpm

[mikey40]

Had my 450 for 12 years now and its not been driven regularly over the last 18 mths. Starts up fine and has the normal stepper motor irregular idling problems now and then but soon settles down. However, when driving at around 2000 rpm in 3rd, 4th and particularly 5th gear it seems to have a subtle hesitancy or misses now and then. Difficult to know if its fuel or ignition issue. As soon as you press the accelerator and go past 2000 rpm it disappears. The normal transmission shunting has got worse as well below 2000rpm. Is this a cam timing, ecu or fuelling issue? Any thoughts or suggestions gratefully received!
Been thinking about an ECU upgrade, would this cure the above running symptoms?

[NZ fan]

I'd say fit new plugs if not done recently, check leads and extenders for arcing/corrosion and continuity, same for the rotor and cap, fresh fuel and use it more. it may be smoother with a different engine management system [especially if it controls the ignition] but lack of use introduces stale fuel, moisture and corrosion that will play havoc on most engines. oh and congrats on owning it for so long i hope i still have mine after 12 years!

[jojackson4]

As above + coil and amp they tend to go on held throttle