Gear oil and transmission fluid.

My Raptor has been in some moderate to deep water crossing in its early life. It seems like after this last freeze cycle we just had the the rear end is locking up more then it used to if that makes sense. So I'm planning on changing the both diffs and the trans. I was thinking about putting Royal Purple in the diffs and the a better Ford option if there is one in the trans. Anyone have any thoughts on this.

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Might as well do the transfer case too...

I think you'd be fine with any good gear oil that meets Ford specs for the application. For the transmission with its complex internals, I'd stick with the exact fluid recommended by Ford.

I've heard horror stories of people buying or dealerships selling them the wrong trans fluid and it destroying the trans.
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My neighbor brought his nearly new Honda CR-V to the local SpeeDee lube and they put the wrong fluid in his transmission. Tore it up pretty good. Cost SpeeDee a new transmission.

Stick with the OEM products. Can't go wrong and will defend any issue down the road. I think a lot of the after market stuff is more expensive, but not any better. Just my .02

Ford OEM oils and lubes are actually quite high in quality. IIRC their engine oil is actually manufactured by one of the companies making one of the most reputable highest ranked oils around.

Like others said, I would stick to the FoMoCo stuff for not only quality, but also pricing and warranty reasons. FFS