Transmission issues

Hello, I am new to this forum. I have a 2002 Celica GT automatic and it wont shift out of what seems like 3rd. The car starts and runs fine and reverse works great but when I put it in drive it seems to be starting out in 3rd and will not shift out of it no mater how fast or slow I go. I tried to manually shift from low to 2nd and then to drive and nothing it still starts in 3rd. Any ideas as to what may be causing this? Thank you in advance