Rebuilt 727 slow to no engage

If it doesn't engage into both forward and reverse it's possible something is put together wrong in the valve body. The only problem is you have already revved it to the moon and back trying to get it to engage and that most likely smoked the clutch packs so i'd take it out for a complete inspection. Your only saving grace for the clutches is it could be a broken torque converter. Was this a working trans/converter when sent to the shop for a rebuild? If it was you can most likely rule out the converter