My 1995 4l80e trans will shift into third only when i floor it but when i let off throttle it seems to go to nutrall and help would be appreashed

try adjusting the throttle pressure cable located at the throttle body. push in the clip that holds it, remove floor mat on drivers side and fully depress the gas pedal
(engine off of course) then release the pedal. the clip should go back to lock position. all this is on the assumption you have the Asian warner aw4 transmission but the procedure is similar for the chrysler trans also

check the fluid level
check those with engine warm, idling and gear selector in neutral
check the Throttle Pressure Cable (it is attached to the throttle body and goes down to the trans) - open the throttle body manually all the way (Wide Open Throtle) the TP cable should have all the slack taken up. From your symptoms I would expect to see the cable end disconnected from the throttle body. The plastic end that clips to the throttle body gets crispy and breaks. I have in the past used a couple tiny plastic ty raps to hold it in place on the linkage. If you choose to do that temporary repair - Please carefully inspect the throttle body to make sure the repair doesn't cause the throttle body to bind and not work smoothly. Done improperly the throttle body can stick and you will have a serious problem if that happens.

a/T trans,
does it fail to shift to 3rd with light throttle and flat ground moving say 45mph? Y/N.
trans diagnosis is complex , so is the trans.
it a hands on deal too, with tools.
1: is modulator valve working?
2: is Kickdown cable not stuck at WOT?
3: is filter screen clean?
4: is A/T pump pressure at spec.?
the car has an FSM and in this book , as a section called, on car repairs. for A/T . its 100% on topic.

Check the wiring headed intot he transmission, if all good, remove the pan and check the interior,. of all good, then you can bet that you will need to replace the shifting solenoid in the tranny and you'll be good to go...
Best regards
Ck

your shifting cable is weared down it will go bad .

Its NEW? take it to whoever you got it from. The problem may not be IN the trans, but a trans shop need to check it out to see why its not going into overdrive.

THERE SHOULD BE A CABLE THAT GOES FROM THE THROTTLE BODY DOWN TO THE TRANS MAKE SEE IF IT IS NOT MOVING THEY WILL STICK ON THE TRANS AND THE CLIP WILL BRAKE AT THE THROTTLE BODY

get it serviced as the valve body might be sticking from lack of use!

Could be the Trans Computer , I Think it lives behind the center console (bolted to the floor).
There should be 2 computers 1 Trans the other Engine.
Let me know how you get on.

Are you sure the TV ( trans shift cable at the throttle valve) cable is correctly adjusted?? Without line pressure readings, I can only guess that the D3/Part throttle check ball is missing, if it is a trans problem
If the TV is correct, I am assuming that the TV cable is pulled tight at WOT.
Did you check the throttle (ACCEL) cable to be sure that the carb goes wide open when your accel pedal is on the floor?? This must be done with someone in the car and a second person looking at the carb. Without doing this, you do not know if you have WOT. Without WOT, the trans will not de-tent and shift down.