4.6is won't drive in any gear or hold in park...part deux!

[shebuilt]

Well I am back fellow lovers of our X5's.

In 2016 my beloved X5 while driving on the freeway decided to no longer use gears and I ended up changing my front shaft. Splines looked fine to me on the case, so I put er in and drove him another 10K or or so (not my main driver)...

now as I was driving - bam, yet again he decided nah, not into the gear thing anymore - and I coasted to a park.

Won't engage in any gear, no smoke, no noise, and won't hold in park.

Before I put him up again, can this really be an issue of the case or possibly the rear shaft?

Any previous similar experiences please chime in. It does show trans fail safe, but it did before as well. could this be transmission?