727 No forward or reverse

What about the torque converter? Is it the correct one and known to be good (new doesn't always mean good btw). I've seen converters break internally and when that happens you lose all motion

X2, if all is as said I would have to suspect the converter.
Either the wrong spline, or broken inside.

If one knew what they were feeling, turning the direct drum with the VB off might show something. (maybe)

No odd noises?