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I'm guessing this would be the breather?

Yep.

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There's also a hose coming off the front, right behind the driveshaft, that runs along the frame toward the firewall.

Hose or wire cover? I think what you are describing might be the wires for the ABS. I'm pretty sure Cragdweller said his truck had this setup before he swapped his gears. If it really is a hose, then I'd say you have a locker <img src="/forums/images/graemlins/cheers.gif" alt="" />. 4.22's are probably good for up to 31's. Over that, you may want 4.625's from a Monty so that you don't hurt your drivability <img src="/forums/images/graemlins/kewl.gif" alt="" />.

'06 Dakota QC 4.7 6sp 4x4
'88 Mighty Max
'77 KZ1000 fun old bike