Issues with an a9l

[Mopac]

Im having a problem tuning my own car, is a 347 stroker with about 420hp, 30lb injectors, 76m c/l meter, long tubes with a 3" exhaust. I am having issues ironing out the top end of the tune. At about 5000rpm, the car litteraly drops 20hp for 500rpm and then comes back on to complete the HP curve. It litterly looks like a U in the top end of the chart. I swapped to a lightning mass air, and it still has the dynamics of the last passes. No matter what i do, i cant change the dynamic of it. Car runs a clean 12.8 down low, and drops to 11.8 at the dip, and then back to 12.8. Graphing the new meter proved to only go 4.4V at the max. My timing is locked at about 23' and 14 base. Is there anything in the tune that may have to do with this problem? i have changed springs, and tried all kinds of lifter pre-load thinking it may be a harmonic or a lifter pump up, but why would the power come back on?? any help would be AWESOME as im losing my mind with this!

[sohfast94]

I know it's late. But assuming you may not have solved this already. Do you have a dyno plot and log?