A friend of mine has a fresh built aftermarket cased ATI. Everything in the transmission is new, but it will not shift into second gear. First, reverse, neutral, and park all work as they are supposed to. He can put the trans in neutral and slowly pull the shifter back to drive, and it will slowly start to move. Any help would be greatly appreciated.

Couple things I would recommend checking

First make sure that the shifter is adjusted properly. Make sure that with the shifter in drive and the selector shaft in drive that the pin on the cable slides in and out easily.

If that is good it may point to a more serious issue. I know personally I have torn a pump ring installing the front pump. I was lucky enough that I was not happy with the end play and had to take it apart so I found my issue before it caused a big problem. If a pump or input ring was torn during assembly you could have low pressure on the direct clutch pack.

Those are the things that come to mind for me. Others may have additional suggestions.

Check the roostercomb inside the trans for cracks, and or loose on the splined shaft.

The problem has been located. One of the snap rings that goes on either end of the plunger in the valve body was found in the pan. Thanks for the help

That will do it too. Glad you found it.