700R4 no pressure when cold

[Consaka]

I have a 1984 diesel van with the 700r4 transmission. This rig suddenly started not moving when cold. No gear did anything till it was allowed to warm up. I put a gauge on it and it literally has zero pressure when running cold. After 15 minutes or so when it starts warming up the transmission will gradually start showing an increase in pressure. At about 30 lbs you can move it and I believe all gears will work. If allowed to get hot you might see as high as 60psi. needle on the gauge jumps around a lot. I pulled the pan off but could find nothing obviously amiss. I figured maybe the pressure regulating spring had broken but it seems fine.
Thoughts?