1125 code issue

[afcamaro]

Ive swapped an 05 5.3 into my '72. It has the dbw, and everything from the swap came from the exact same truck.
I am still getting issues about every 2-3 times I drive it it will throw and 1125 code. At that point it will go into limp home mode.

It drives great, until it throws that code.

Any ideas on what this could be? It has always seemed to do this, but is getting worse and worse.