Supercharging issues ( charger or tuning )

It has been awhile since I had posted here and hopefully someone might be able to help. I have an 86 Mustang, and running a new setup which is using an old Novi 1000. Anyways, I am in the process of tuning and started to finish my tuning up with WOT runs. While doing my runs, I'm noticing at 5000 rpm, i lose power and the car seems to fall flat on its face. It only when I'm in boost, when I'm driving at part throttle, or WOT without the charger I don't have this problem. The novi 1000 is pullied with a 3.00" pulley with a 7.00" crank.My engine setup is a 306 with a Holley Systemax 2 intake, AFR 185 w/ upgraded springs , FTI custom grind, 42# inj, 255 pump, and aero motive fuel regulator. Thanks and if more questions need to be answered let me know.

what is the boost @ when this happens?
what is the fuel pressure @ when this happens?
what is the spring pressure on the seat?
weak valve spring, valve float, low fuel pressure, belt slippage causing loss of boost?

Sorry it has been awhile. Let me see what I can answer. The boost seems to about 7# of boost. The springs are the red stripe. They rated it at 412# @ 1.210, from AFR specs. We went with those spring at recommendation from the cam builder to avoid valve float. The fuel pressure is set @ 39 psi. Have a gauge on the AFPR but it is visible from the engine bay.


now at the time I posted this originally, I think I was dealing with belt slippage, notice later on one of the idler pulleys came off.
now I fixed the pulley issue, but the boost cutting off is doing it again. ~4700 rpm in 4th and ~5100 Rpm
in 3rd. I have everything tightened but it almost seems like it could be belt slippage. Using an 8 rib setup 3.00 pulley and 7.00 inch crank.
If it helps, spark seems to be retarding to 24 degrees when this happens. At this point I'm just trying to find awswers. I'm gonna check the spark plugs to see where my gap is at. I'm at a loss.

Also, dunno if this helps but my Novi 1000 is an older unit, discharge outlet has the divider in the middle