Ok I checked for vacuum leaks with the carb cleaner, and there are no problems to be found. So now that that is rectified, I went ahead and performed those diagnostics you mentioned. First I set the idle so it was stable and not too rich, then pulled on the throttle until it went lean and wanted to die. Pumping the accelerator pump while not moving the throttle at this point definitely made a huge difference, it increased the RPM substantially and eliminated the sputtering, then after a couple seconds it returned to the dead lean state again. I also tried this starting from a higher RPM point and dropping the throttle to the lean condition, and it basically did the same thing. The wierd part is that plugging the air bleeds (the bigger ones on the outside) didn't really do too much to help the problem, although the best I could do plugging it was two small hex keys, so I doubt if I sealed the bleeds off entirely. The choke horn was in the way and I couldn't get my fingers to cover the holes too well. If I need to totally seal the bleeds to have an effect, I will come up with a better way to do this next time.
Also, I fixed the old 650 Holley that this Demon is replacing, and I put it back on for a bit and it worked great - so no vacuum leaks for sure. If for some reason I really need to get deep into the Demon to find the problem at least I have a backup so I can drive my car
I bought a rebuild kit for the Holley and I still have two bowl gaskets and two metering block gaskets left over so if I need to tear into the Demon repeatedly I at least have backup gaskets.
Thanks for the help so far, and if there's any other suggestions please let me know.