I have a 4L80 swap with the PCM of NC box. Sometimes when I take off it wants to start in second gear but then if I give it more Throttle and it will shift back down in to first and operate normally, today it started to do that again and now I only have second gear and third gear with lock up. No first no overdrive. No codes. Has happened a few times it typically goes back to normal operation. I just took off from a light and overdrive came back. The next light first was back

 

What's a NC box?

What are the trans mods? Was it rebuilt recently?

 

The PCM of North Carolina box is a plug adapter that connects the 4l80 trans to the 4l60 plug. Trans has 15000 miles on it and runs great 90% of the time. This intermittent issue just started about 2 weeks ago, and only shows up once in a while.