I am building a custom tail light.

Daz1712:
Cant see it mentioned but you have run a 5v regulator into the Vin which runs to the input of a 5v onboard regulator.
>>> Run it to the 5v <<<

Actually (I) wouldn't do that.

The on-board regulator provides you with an extra layer of supply protection.
I'd rather get a clean +9-12V (nominal) into the +VIN pin, and go from there.

For the block of LEDs, I'd use a similar arrangement (bulked up to support the higher current needed)

Finally - I'd seriously look at the WS281x LED matrices. Easy to develop, and all the brains are within the actual LED chips.