This is baffling me. In first gear, around 4k rpm it feels like the engine hesitates at WOT for s split second. Only at WOT, and only in first gear. Could this be the TCS?

Its almost like hitting a rev limiter. The tach freezes for a slight moment then keeps pulling hard to redline.

Any ideas?

could be the traction control system. is there a warning light that comes on to tell you the traction control is working? have you tried doing it with the traction control off?

The traction light hasn't come on, but it almost feels like the tires are breaking traction. Wouldn't that be more likely to happen more toward the take off than at that rpm range though? Its consistently at the same engine speed every time.

I'm going out in a little bit, I'll try without the control on

Be sure to hold the button for a few seconds. You should see 2 lights come on, indicating the TCS and VSC are both off.

at about 4 rpms is when full torque hits, so it makes more sense that traction would break there when you're in the lowest gear with the highest torque output.

dual vvt-i. its the computer changing the cam timing to produce more power, you can really hear it with a cai because it really starts opening up the air flow and adding fuel. and yes, it will break your tires loose. if your on a slick road itll also do it in second. just press and hold the traction control button. trac off' will appear immediately, and after about 4-5 sec the traction control image will appear also. you shouldnt have a problem with it after that:)