Trans appeared to be working fine till a recent restart. No unusual noises, shifting ok. Moving into drive or reverse, gives no action or noises. I had checked the fluid level the day before. I attached a pressure gauge to the test port that's beside the Vacuum Modulator, resulting in zero pressure reading. Approx. 2 months prior I checked the pressure and had to increase to the 40 psi from ~25 psi level. I can see the Torque Converter turning, so not a disconnect there.
Prior to this new issue engine speed would always drop from 900 rpm to ~ 500 when moved into drive or reverse.
Engine is strong M110 with 170psi + cyl. pressure.
Can anyone give some possible causes or suggest any additional tests before pulling trans?
An auto trans is the only component on a car that I've never rebuilt. There's alot of good info available to follow on this site & others. I'd prefer to learn a new skill & rebuild myself. I'm sure there are good trans specialists close by, but don't have a good recommendation for anyone in Seattle/Portland area

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80 280TE, 5 speed
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