New truck/tranny problem
 

A buddy of mine bought a 2001 dodge cummins this past weekend with the auto tranny in it and for the last few days it drove great but today 2nd gear seems to miss all the sudden. In first gear if you wrap the engine to redline and back off the throttle with will shift into 2nd, once its in 2nd it doesnt slip or anything it just wont go into 2nd under load. Any ideas? Any help is very much appreciated before we start throwing parts at it.

First thing I'd try is a fluid and filter change and adjusting the bands.

Amy codes?