Cleaning or checking/changing the fuel filters is definately a good idea - a restricted fuel delivery problem will definately be more prominant under load.
Shorting any coil ballast resistor fitted would be a good idea, although I would guess you have none fitted if ignition is controlled/fired by ECU.
Injector failure is always a possibility but less likely in my experience unless you've managed to allow debris into the fuel rail and as it's managed some 7000 km reliably thus far I'd still think they are ok - esp if the quality of idle has not changed at all.
If you hook up the laptop in the passenger seat (no I don't recommend looking at it whilst driving) - start up, go to the diags/errors page - rev up a few times to ensure no errors are reported off load - go for a drive - and once back or pulled over, have a look again at the screen to check for no reported errors. If you have hall effect triggers/pickups, it should be possible to have a 'spirited' drive with no errors indicated at all. In my experience, mag pickups will always indicate the occasional error but will not normally affect the smooth running of the motor.
Let us know how you get on..