94 325is Transmission is stuck in third

I have a '94 325 with 150k miles. The automatic transmission won't shift into 1st gear to accelerate from a stopped position when it is cold. Most of the time it will shift to 1st gear if it is warmed-up. I had the transmission fluid & filter changed at 95k.
Do I just need to do transmission oil & filter change?
What about adding one of these BG311 transmission conditioners?
Surely someone else has been through this problem and can help me decide the correct course of action.
Thanks for all your help!
Bogatti

Put the shifter all the into first from park with a swift movement when you start it up cold and floor it, if you get nothing but a little bit of push your tranny is gone and needs to be rebuilt/replaced.

Oh, and next time, get a manual, automatics are for girlies!

This weekend I drained the transmission fluid & added all new AT fluids & a can of BG310 transmission conditioner. All the problems with the transmission being stuck in third gear went away. Did I dodge the bullet or what !
Bogatti