So I have a 03 trailblazer, automatic transmission and when you drive forward it will go up to about 1500 rpms and drop back down to 1000 or so,and does so over and over again, it has no power and will only get up to about 10 or 15 mph. The engine runs great and at idle or if you're driving in reverse it does fine. It has no error codes and I'm totally stumped, any help would be much appreciated. Thanks oh and it just started doing this one day out of the blue.