1999 sable transmission
 

i have a 1999 sable with the 3.0 duratec 24 valve engine. it will not shift untill it hits between 4.5 to 5 thousand rpms and hesitates before it shifts. if i get off the gas then it will shift. if im going up a steep hill it will down shift and the rpms will increase dramaticly. does anybody know what it could be. thanks alot