I believe both diffs and transmission have breathers. My rear diff's was dry rotted so just replaced it with some hose from Autozone. I think rather than extend that one you should just replace it - it's pretty short anyway. I don't recall exactly where the front diff and transmission breathers vent but just look for a couple of open ended hoses in the engine bay, or trace them up from the diff / trans. Again, it may just be easier to replace them than extend them. Are you planning on fording deep water? I never worried about it when I did my lift. Assuming you know that you'll need to modify the hydraulic brake hose mount at the rear axle or else you risk ripping it off at full flex. Not sure if there is a height of lift beyond which you risk the front brake lines? Mine seem OK with a 3ish inch lift.