You can tune above 4200 rpms just fine with any piggyback. 429 whp was not made in closed loop. If all I cared about was open loop, I would have never tapped the O2 and would have had my car tuned the very first night I installed the LC-1, however many weeks or months ago that was.
If you have the car back, and a wideband on your AUX input of the FIC, you should be able to get nice logs like I have been posting, regardless of what plots your tuner gave you.
First of all try, flooring it below 4200 rpms and see if you feel a change in power at 4200 rpms. You may not be able to notice it with your butt dyno, but you'll see it in the Injector Duty cycle and AFR plots of your log. If there is no transition, then your O2 has been modified, and you'll need a scan tool to make sure your trims are tuned out.
If your trims are good (close to 0), then you can try the two scenarios I mentioned before, but they will only cause a problem if your tuner modified your O2 signal for closed loop operation.
1. Take the car up to speed, and put it in a high enough gear so that you can floor it for more than three seconds without hitting 4200 rpms. Look at the AFR and duty cycle plots. You should see a spike in fuel when the car goes to open loop. If your tuner added fuel in the closed loop region to avoid LTFT's (which he should have), then you will run excessly rich until you are above 4200 rpms.
2. The other scenario is when you take the care at full throttle past 4200 rpms, and then upshift to rpms lower than 4200 rpms. The car will stay in open loop even though you dropped below 4200 rpms, and you have the same problem of too much fuel.
I've mentioned this before, but this is a very livable situation. Both of these scenarios are rare and can easily be avoided, but you need to understand what's going on with your trims, or you could pull the battery one day inadvertently resetting your PCM, and then blow your engine because your positive trims were wiped clean.
