Have you had any problems with the IMRC not opening? Could be something to look at as it would cause similar power loss.

99 T-Red SVT #1634/2760 K&N filter Aussie Intake Pipe Pro-M 75mm & Optimizer B&M Edge Shifter Quaife LSD Borla Cat back MSDS Headers/sho-shop Y-Pipe Dynoed at 184.2 HP & 157.2 TQ 14.53@94.15