I have a 95 LS with a 3.1.

Heres my trouble that im having

when the car is cold it works just fine shifts perfect with no slipping at all. After it heats up it i can put it in L1 and it shifts into second with out changing the shifter but will not go into 3rd.

I just changed the fluided, filter and the vehicle speed sensor. Is there anything else that i can look into changing before i have to get a rebuild or am i missing a sensor

any help is appreciated so im open for any and all suggestions