Automatic Transmission Just does not feel right when shifting.

2004 GTO with 52k in miles. Tranny fluid was changed at about 35k. Lately I have noticed that the transmission is not as responsive to high RPM downshifts and also when fully getting up her there seems to be a little lag in shifting. Not much but enough to notice after owning this car for 2 years. I am running a superchip tune on the car. Any advise of what is causing this or this a sign of tranny rebuild and how long do I got?

the tranny could be getting weak, but i have noticed that the 4l60e and 4l65e transmissions always seem a little weird at different points. You only have 52k miles which is not a lot. Hopefully someone else can give you a better answer

You waited until it had 35k to change the fluid? I am changing mine at 10k intervals, fluid is cheap insurance. Unless your trans is slipping or shifting really weird you should be just fine. If the fluid was really dark when changed that could be an indication that it is getting sick though.