Yep exactly like it hits a rev limiter. Seems those asm have problem letting the coils have enough current.
Have you measured the voltage at the coils when it won't rev up? If the RSR ASM is not able to provide enough current, you should be able to see that the voltage at the coils is lower than expected.
If you can show that the RSR ASM is not providing enough power to the coils, you could insert a relay in the circuit and confirm that this solves the issue. I'm not sure a relay is the best permanent solution, but it should work well enough for you to determine if this is the real issue or it's really something else.
What coils are you running? Are you using the gray Dyna 2.2 ohm for the Dyna 2000?
Any chance you have or could draw a diagram of how you have it wired? I'm assuming the DRL400 and Dyna-2000 are working by themselves, and they otherwise play well together? I'm guessing you set the Dyna-2000 rev limiter to be well above the DRL400 high-limit, and let the DRL400 do all the work?
I believe my dad's Z1 drag bike used the Dyna 4000 and the big Dyna coil pack (Twinfire). The Dyna-4000 has an air kill switch input and two-stage rev limiter, but the shifting is not automatic and it doesn't have all of the fancy timing features of the RSR ASM.
His bike also has the Dyna shift light box (DSMS-4), which this manual shows can be combined with the DRL400 to create an auto-shift setup.
shop.dynatekuk.com/ekmps/shops/dynojet/r...m-2h-dsm4-dsm-4h.pdf