what can cause a 4L60E transmission not to shift?

What is your question?

I have rebuilt my transmission put a new valve body, new tcm and reprogramed it. but when you hit the accelerator it will just go to 6000rpm if you put the gas to the floor.it stays in first gear. its an automatic transmission and the truck has 4wd. after I rebuilt the transmission everything was okay but the next day it was not wanting to shift out of first and there are no leaks.

What makes this problem better or worse?

cold and warm

How long has your 2007 Chevrolet Silverado 1500 had this problem?

2 months