Tuning a customer's GT500. Primary mods are 2.4L VMP supercharger and 65mm TB. Tuned it for the first time this Summer, ran great and cranked out 600 RWHP. Car came back because it failed DEQ - rear O2s turned off. Turned rear O2 back on, car passed DEQ fine - but now exhibits strange behavior on the dyno at WOT. Sometimes it makes a clean, smooth pull at around the same 600 number. Other times, it kind of surges, creates a rather bumpy looking power curve, and is down 10-15% in power. The only difference I can see between the two logs is that the low power log is very low in timing all the way up. But the resolution of the Ford logging is pretty low, it might be missing something in the curves ...
I don't know what to try next - I'm pretty experienced on GM tuning, but this is only my second Ford. Attached are logs from a clean pull, and one problematic pull, as well as the current tune. And yes, I do know the MAF still needs work - the first time around, I didn't realize you could change the MAF axes.
Thanks much for any help you Ford experts can give me ...