i'm looking for some answers to help determine why my gt has suddenly become sluggish on acceleration from about midrange thru topend..i'll explain.. my 2002 gt has 65,000 mi. on it. i drive it daily back and forth to work, but u know as well as i that eversooften, someone out there wants to test u..my motor 4.6 is completely stock w/5-speed. i have changed the stock exhaust from cats back to an ARK exhaust, the company is 'arkspeedraceing' out of california. and i use a k&n filter in my stock airintake. when at idle after warming up.. u hear a nice rumble a slight miss 'this is what it sounds like to me' i've had it looked at and was told theres nothing wrong,they all do that, that its just the cam.... i was thinking of haveing it dynoed.... just to see if my rwhp is where it should be.i'm also running 5w30 at present should i change to 10w30 ? how can i find out what is causeing this sluggish performance? any help will be greatly appreciated........