45RFE trans

My friend's 99 grand cherokee 4.7/45RFE has recurring "wrong ratio 4th " codes and has gone into a hard shifting, limp home mode. Nothing in the pan, fluid looks clean and does not smell burnt. We are planning to pull it out, any pitfalls I need to know about on these tranny's? this will be my first one.
Thanks in advance.
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