Misfire or cutout under a load

I have a 2003 grand prix gtp with 116,000 miles runs great under normal conditions! When you put it under a load {i.E. Heavy boost, passing or at highway speeds in high gear it's almost like it's hitting the park limiter. I changed coil packs and module with no change. No codes or lights. Once it gets past a certain rpm generally around 4-4200 rpms it seem to pick up again. Any feedback would be greatly appreciated. Thank you!