If it's not really about tuning or wiring. Then it belongs in here.
The title sums up the question.
If you have a dyno capable of driving the wheels, you can reach all the cells. Certainly most tuning shops don't have that, but OEM calibrators do.
The lowest RPM and torque that can be controlled varies with the dyno, but my Dynapack chassis dyno can hold a fixed engine speed well under 1000 RPM if the engine makes enough torque there.
i found out on a particular race series , when on the dyno [ controlled engine and ecu ] that at the top end they did not make enough tq to run the dyna pac , 50lb tq , it sounded so weird
Try using a lower gear (higher numeric ratio). I tune bike-engined cars and often have to use 2nd gear to to the low torque output of the engine at high RPM.