eb14poppa1

I have two issues with my transmission and really have no idea where to start. Whenever i shift it into overdrive it completely slips. When i have it in drive it shifts smooth and nice up to third, its just when in overdrive when i have the problem. The other issue is that when im slowing down or when i want to pass someone or make it up a hill the thing doesnt want to down shift. It will shift down to first once i get to about 15mph, but nothing till then. It wont even downshift if i stomp the gas all the way to the floor. Was thinking it might be the transmission speed sensor or the throttle position sensor, but im not sure. Any help would be appreciated.