if you are using a t25 turbo, the cat back would make it spike some, t25s are hard to keep from spiking, i gave up on mine, i spiked it hard and ran it harder, the thing was pretty much dead at 50k.
laters
dave

2004 white mach1
k&n fipk,Meziere w/p,mac headers,o/r prochamber, bassani c/b, ported heads&intake,php 3/8" spacer,accel coils & hardcore wires, comp 106400 cams,03 cobra flywheel&clutch,456gear,FR 31spline axles & center diff. steeda shifter & quad adjuster

2001 svt lightning
magnaflow C/B,4lb lower,accufab t.b.,lfp E fan, FR waterpump,punisher VB,obx headers