5EAT wont shift

after a driving the car a bit rough last night the trans wont shift from 1st to 2nd while in auto it only shifts at redline. to avoid this i started driving in sport mode which works just fine. i can also move the shifter to sport mode then back to auto and it will shift normally until the trans returns to 1st gear by slowing down or stopping. i have searched for hours for similar problems and havent found anything. can someone please help btw its stock 06 gt with 50000 miles

i have a warranty but would like to take it in with an idea of what might be wrong