y-pipe in an auto

I have an '98 gle (hence auto) and was wondering how much of a difference a y-pipe would really make. I've seen dyno results on other maxes and it seems like there is actual hp and torque loss around 3200 rpm, but then significant hp and tq gain past 4000 rpm. In my auto, i notice that it downshifts around a little past 3000 rpm to a maximum of ~4000 rpm, then drops back down somewhere near 3000 again. It seems like adding a y-pipe will only cause and increase in power during downshifting, and possibly a loss of power when driving in the upper power band of normal cruising. It seems like the ypipe in an auto would just be taking power away from one area and placing it at another, and therefore takes only a little advantage of a y-pipe's potential. Any thoughts?

dude a y pipe makes it feel like a different car. regardless of what tranny you have 17 hp is 17 hp.
it's like a 3 hp loss at 3k rpm and at least 5 hp everywhere else all the way up to 33 peak hp and an average of 18 hp and 19 lbs torque.

this shows 18 hp gained
http://www.motorvate.ca/auto/maxima/ypipe/images/ypipe_comp_ro_hp.jpg

this shows 19 lbs torque gained
http://www.motorvate.ca/auto/maxima/ypipe/images/ypipe_comp_ro_torq.jpg

this is an all in all good maxima site http://www.motorvate.ca/mvp.php/504