Nice!

I am sorry to say it... but DIY builder error is one of the most common causes for transmission issues.

Double and triple check your work.
Air check/ test everything that you can.
Make sure bushings fit over the mating component before driving the bushing into the part it is intended for.

If you do not have a trans-brake... and have all stock parts for Low-Reverse...
And the Pressure Regulator Valve Boost-Valve and Sleeve are not worn...
I would consider deleting the Reverse-Boost circuit.