Auto will not shift out of P when cold.

I have a '93 Ranger, automatic transmission - OD (bunch-o'-miles on her). Started with being slow to engage in any gear out of park when cold. Once the truck is in gear and driven a bit, it runs and shifts fine.

Has gotten to point where it doesn't engage at all (before the end of my patience). I had found a description of this before ...

What is most likely the culprit, can it be corrected w/o a overhaul??!

Grumpy