the auto tranny is limited to 6464 rpms mine usually shifts at 6350 to 6400 but you'll never know exactly because you guages could be off a little. i got indiglos so maybe they dont match exactly with the stock layout so it seems like it shifts sooner. but to ur question maybe it shifts early because ur T.B isnt opening all the way so the throttle position sensor tells the tranny to shift earlier. take off ur intake have some1 floor (car off) and check to see if the Plate opens all the way