727 No forward or reverse

Having lube pressure means the pump and TC are doing something. It varies from about 5 to 30 psi

Just so you know; when reverse is selected, every other hydraulic circuit is shut down, except the L/R servo and the hi-drum(front clutch), and the pump is running wide open, unregulated. Checking the pressure at the L/R servo can see pressures of 235psi or more at 1000rpm. This will prove that the pump is working and the L/R servo is engaged.If it still does not move, I would suspect a problem in the hi-drum or stripped splines on the planetary.But since it also does not move in Manual low,(which uses the same L/R servo but uses the rear-clutch) NOR move in drive-low ( which uses the rear clutch and the over-running clutch),and the air-pressure tests were good, I would have to suspect the stripped planetary or the over-running clutch.
I would be doing a complete oil pressure test, looking for line pressure of 54 to 60psi at 1000 rpm@ oil-temp of 150 to 200*F. Line pressure should rise to near 100 by increasing the TV/KD pressure at the disconnected KD lever.
If you have these pressures, but no output, then it's back to the stripped spline idea, and complete teardown.
To me this looks like a mechanical issue,with a failure of the outputshaft to receive torque from the front end, or a failure of the TC to transmit torque from the crank in the first place.The pressure test can only prove so much, in this case.But you gotta start someplace.........