Just replaced 2 upstream O2 sensors (BTW use DENSO, not BOSCH). No codes for 2 months now (knock on wood).

But:

1. In neutral rev up to 3 K rpm - runs OK - give it a little more, starts misfiring!
2. Put in gear and drive, I can now can take up to 5.5 K rpm
3. Monitoring Fuel pressure at rail; 39-40 PSI at idle, 57-58 at WOT. Hose from fuel pressure regulator to Intake manifold is good!
4. Monitoring A/F ratio using OBDII reader and Torque app - at Idle 13.7- 14.3 AFR, hit the gas, AFR goes to 18-20, Engine knocks, I back off of course.

5. Cant find any vacuum leaks! Put hose clamp on at air inlet tube/throttle body junction; thought as S/C drew air in harder, more air might be getting past TB seal. Airbox to air tube (just past MAF) also nice and _very_ snug.
New test drive shows same problem still there!!

6. Any advice from the hands on tuners or pro mechanics? (Please, if you don't work on engines keep the guesses to yourself - I'm already good at that, Thanks!!)
7. Where else should I look for vacuum leaks? Oh, I also put some Lucas Injector cleaner lubricant, the thinking being Injector might be stuck closed.
(8. How often does this really happen ?)

Thanks!