I have a 2003 2500 Cummins with a 47re Transmission.
A few mounths ago I had problem with it, it didnt move forward or reverse, I changed the filter and oil, I also adjusted the front and back band and problem was solved (Clogged filter)

Now it started to delay 3rd gear when transmission is warm, no problem with cold enginee/transmission.

Anyone have an idea?

Edit: Fluid level checked OK

 

It's possible the lack of fluid may have damaged the clutches. You could drop the pan and look for excessive material. It maybe tome for a new trans.