May 25, 2016

My 2000 Chevy Silverado 5.3 automatic has always idled on 500 in park and when I come to a stop in gear but it has been idling sometimes around 700 or 800 at different times lately. When it`s idling higher than 500 it always takes a little longer for it to change gears. When it`s idling higher and I put it in park it goes up to 1000 or a hair higher. Can someone tell me what I can try to fix this problem? I do not have any error lights showing on the dash. Thanks for any help.
Donnie