Ive searched this forum and a few other forums and cant quite formulate a plan of attack for what im sure is a running rich problem. Here are my symptoms:

Gas mileage avg low 15-16

engine sounds gargly and late to respond with WOT, especially in 2nd and 3rd gear

idle is lumpy and wont stall but does not seem "normal" as compared to other Z's ive sampled, however OBDII says im idling at 650 which is the norm +-50

Ive done the entire relearn 16 million times, including hard resetting the ecu with battery unplugging etc

Heres what ive done so far:
Checked for vaccum leaks in all the seals and hoses x5 AND replaced PCV
checked the injectors
checked and cleaned the entire plenum assy
replaced the TB
checked coolant levels and flushed radiator
replaced plugs with ngk reccomended
checked exhaust for leaks, found one and replaced the gasket, no avail

I bought two upstream o2 sensors for this weekend and I am going to replace them both, but I'm at a loss and i dont want to keep burning cash trying to figure this out. I really like this car but I want to know whats going on? I know I could just buy uprev and tune it out, but that seems like a last ditch effort. Any ideas?

About the car: 2003 with 60k miles, JWT popcharger, motordyne 5/16 spacer, injen SES cat back

Thats all i got. thanks guys

 

What sort of driving do you do, and how aggressively do you drive? I wouldn't consider 15-16 mpg abnormal for aggressive driving, short trips, stop-n-go, etc. It's pretty bad for legal cruising on the interstate, though.

I'm assuming there's no CEL or codes to give you a clue, just low mpg.

 

I don't drive too aggressive and I take very short trips. There are no cel codes to tip me off, its that feeling you just know something is wrong.