Help new me with my new 530it

[boom2085]

I found a 1994 530it with the engine replaced that had all the papers for everything and was not too far to drive it back. It ran fine for the 1200 miles home but the day after I got back I had to get it smoged checked on a dyno and after that the ABS and the traction control did not work. After letting it sit they started working. And them latter on that night I got the trans program message. Could the guys at the check station have messed it up or could it have been cause of the cold (about 25 degrees out) it only does it after it has been driven for a little.
Tell it errors it drives fine no slipping until right before it happens then it go out of gear and comes back with a boom if I did not notice and taken my foot of the gas and then it go to limp mode. Now I guess what I am asking how do I pull the codes out and find out what wrong. Thanks to any one who cam help.

[632 Regal]

low battery voltage is a common cause of the trans code message. There is another thread on this from a few minutes ago.