Lagging issues

[clean2g]

I'm having some annoying lagging issues and also a mushy clutch pedal that lasts for the first 10 minutes that I drive. I have changed everything humanly possible that I can think of: Clutch master and slave cylinders, SS clutch line, transmission was rebuilt 8,000 miles ago and new clutch was put in 20,000 miles ago. The lagging is not consistent; some days it's there some days it's not. I can't figure out if the clutch is slipping or if there's a boost leak. Right before spool up there will be an obvious lag/bog and then the turbo starts spooling. The car is a 97 GSX with 108,XXX miles. Mods are: Shep stage 1 rebuilt trans, ACT 2600 clutch w/resurfaced flywheel, mbc, catback exhaust, bov, intake, hahn sidemount ic upgrade, and ic hardpipes. Any advice/input greatly appreciated.