Didn't want to quote FnF, but i don't know how else to explain the problem. When accelerating hard in any gear, except first, I get a momentary hesitation at about 3200-3300 rpm. After that it pulls hard and cleanly to redline.

This started happening after I cleaned my Stillen intake. I had disconnected the battery while doing so and my ECU was reset. I was throwing the dreaded P0420 code for about 15k miles, but I did not have any driveablity/power problems and consistently got high 20's mpg (60%hwy/40%city). I assume that it is just a bad rear O2 sensor.

I have 93k miles on my car. Spark plugs were exchanged at 66k for NGK iridums. It feels almost like a VTEC switchover. After the momentary pause the car pulls harder from 3500+ rpm then it did when I didn't have the pause.

What would cause this momentary pause?