From what I can gather, the 7254 and the 5254 use the same motor and are basically the same, but the 7254 is a little bigger, with a greater 3-pt. lift capacity and a few other things.
The 7254 is discontinued, and I couldn't even find any mention of it at all on Cub Cadet website. The dealer told me that the 5254 is essentially replacing the 7254.