Losing Power, where from?

[Jehu]

I seem to feel my foot hitting the floor with less response than that to which i have become accustomed. I don't see a huge loss in gas milage but a few weeks ago after adding a can of LubroMoly Valve Cleaner the CEL came on for a few minutes a while after. Could that stuff have dislodged enough crap to have clogged the cats perhaps which may be restricting the flow thus resulting in this dimished sense of power? I checked the air filter which was OK , Changed Fuel Filters still the same. Plugs were Denso irisiums about 80,000 miles ago so maybe they're due. Have yet to change the O2 Sensors so they have at least 100,000 miles on them but I read about Vacume leaks and some Plate somewhere but can't find that thread. I checked the duct from the Airbox to the MAF for cracks and its intact. The MAF is pristine. When I changed the Plugs a year ago a few Boots had oil in them. The Previous Owner said he changed the VC gaskest right before I bought so I didn't check them again to see weather the oil leaked pre or post that but I will check soon. Somethings telling me an exhaust issue maybe a hole in the exhaust somewhere or blockage. I had some hesitation a while ago that hasn't gotten worse but had to come from something and the other day I thought I heard engine knock ,always used and use 93 us octane. I have an appointment for the Indy June 11th but I'd like to check what I can myself before I ask him to check everything else. I'll probably chanmge the plugs before then and go back to Bosch Coppers and if I find oil in the boots have the VCG's changed when he does the Timing Chain Cover Gasket fix .