It runs and goes at 55mph she goes around 2500rpms as this happens i downshift to 3rd manually and it's like i did not downshift no difference what so ever so i don't think it's not going into 4th gear at all

 

I noticed something today I accelerated today slowly and counted the shifts it does goes all gears but at 40 it goes back to.third I keep on speeding to 55mph and its doing a whining noise I let go of the gas and the rpms go down to about 1k but if I downshift manually to third the rpms go down gradually with the speed of.the car like turbomonte said could it.just be the converter?